IIRC, I believe the Tessel guys are abandoning the transpiler approach in favor of slightly more powerful hardware for the next generation that can just run node directly... We're really at a point where for the types of projects people want to run for under $100 of hardware, it's fast enough to do a lot more.

Power is a bit of a concern, and it all depends on the environment... being able to get every web monkey coding in more environments is a big win for enthusiasts and commercial applications for limited scope projects... Hell, without a screen or antenna powered on all the time, you can get a lot of processing done on even a smart phone from two generations ago.