Ok I'll have a bite at this one ;-)
In the recent time I really got the impression that the community shifted strongly towards experts. Perhaps the really great shift towards the open source intiative makes everything harder to understand.
Clearly this statement packs a lot in and maybe it should be unpacked a little:
1) Forget if its opensource or not, its moving from individually written pieces of code to code that needs to fit into modules, not only that but it is also recognised that the code will be built by a variety of folks. The same issues would occur if this was proprietary or opensource i.e. the code requirements and inter-operational overheads increase. I think your actually saying moving to a modular code base makes it harder to understand?
2) Xmos as far as I am aware has always been oriented towards the expert, I have seen little evidence of any shift in that positioning irrespective of the addition of the github repository. As far as I can tell the original Xmos codebases and the xlinkers codebases are both still there, github is additional. I will also add that Xmos tends naturally to produce overly complex offerings to support their chips whether that's code or hardware, most of the development kits are over designed and over priced. Much of their software is overly complex just take a look at the network stack which traverses several programming languages and god knows how many programming styles. In contrast the Arduino team (mention by Interactive_Matter) takes a very different approach they strongly believe in learning from beginners over experts and have adopted this into their culture, they also prioritise beginner features and function over expert, I mention this for 2 reasons: firstly its opensource but yet far more approachable then any of proprietary MCU platform, particularly for novices and beginner and secondly I would be stunned to see Xmos take a similar view because everything I have ever experienced with them shouts out EXPERT, I would say that they actually revel in this high mindedness. I don't mean to be purposely hard on Xmos but that's just the way it comes across and I don't see much effort to make things easier for beginners.
Here's an off the top of my head list of stuff that makes Xmos hard for beginners:
1) Software - Mixed language base ASM,XC,C,C++ supporting different languages isn't a bad thing its actually a good idea. However creating modules using mixed languages and mixed programming styles throws beginners under the proverbial bus. My suggestion would be to stick with a single approachable language for all of the basic modules. I would also choose a language newbies would have a chance with - C. Expecting folks to have to learn XC before they do anything is like having a bouncer on the door turning you away for wearing trainers. C is probably the best common denominator and can support all of the required functionality (Or it would if Xmos supported it properly which should be trivial for them I'm thinking builtins and such).
2) Hardware - Ok its time to build my 1st Xmos board lets look at the obstacles thrown in my newbie path: Packages, damm it nothing through hole only surface mount bugger OK smd it will have to be. What are the packages ? G4 BGA ouch not a cats chance of me doing that, L2 WTF double row QFN and minimum 4 layer board lets forget that option what are we left with? L1-128 pin OK looking better, hold on 0.4mm pin spacing dammit can't use my low cost prototyping services then & how did they choose the pins using a dartboard? Lets try the next package L1-64 Ok that looks more reasonable ah oh see a bit of a problem it has a ground paddle that limits me to stencil and hot plate or perhaps more specialised kit like heat pencil grr. Ok lets assume I can somehow overcome the paddle thing (I'll convert my toaster oven) and lay it out. Dammit needing all of these decoupling caps around the L1-64 makes it near impossible to escape the signals without moving to tiny vias and track spacings, thats blown out my cheapo prototyping PCB suppliers again. OK one last go L1 48pin OK its got a paddle same issue as the 64 pin but I may be able to get around that using some hacking techniques and a hole in it. wow there still a lot of decoupling caps but I may just be able to get the signals out, better than the 64pin that's for sure. Right what else do I need? Flash Oh really doesn't it have any built in I thought it was an MCU? so lets add a flash chip and another decoupling cap, bugger I just lost pins, oh only 16 single bit pins? but can't I use them all as single bits? so now down to just 12 single bit pins then.. anything else I should know about? Dual power supply, Oh 1V for the core and 3v3 for the IO, so I need 2 regulators, what they should be switch mode? I'm a newbie I tend to use linear LDOs if pushed, anyone provide me with a decent circuit for the power supply side? Wow Xmos sure use a lot of different PSU chips, looks like every board and kit is different, I'll just randomly pick one and copy it.. Ok I'm done then?Oh of course I nearly forgot the clock I'll just add a cheap resonator, Oh no examples, how about a crystal hmm have to built my own external pierce oscillator WTF why can't I just add a crystal like other MCUs and what is one of them anyhow. OK so I have to add one of those teeny tiny 2 gate inverter chip that's near impossible to solder by hand with the crystal, surely I'm done now.. ? Power supply monitoring and power up sequencing what the hell is all of that? so two more teeny tiny chips that I haven't a clue about. Right I also need a boot loader nothing clever like JTAG programming, Xmos supports USB so I will use that. Oh I have to add a USB chip I thought Xmos was fast enough IO for basic USB, Oh its a tiny qfn chip Oh what joy as if my boards isn't difficult enough, well I will just have to convert that toaster oven then. Right now I'm ready to rock, what no virtual com port over USB but what about my printf debug? no programmable bootloader support your joking. That's not the worse bit OK let me have the bad news, Really my pins have been used up because of the spi flash and USB AARGHHHHH OK I give up I'm going back to my Arduino.
I think you get the picture and its not about being opensource IMHO ;-)