Sure, the cutting edge stuff will always be in the realm of experts with funding, but the pace of progress in technology is such that there seem to be plenty of opportunities for innovation from the grassroots level, serious amateurs and hobbyists.
It kinda feels similar to the early era of personal computers, where anybody with interest and ideas could enter the field, learn things on their own, and even contribute to its advancement.
Further, building a modern full scale General Electric GE90 is extremely far beyond what a hobbyist can accomplish. If anything the true cutting edge is getting ever further out of reach. A few peasants could build a full scale trebuchet, good luck getting your friends together to build a F-22.
Still, it shouldn't be that hard to make a small version of Big Dog technology now. They put a lot of money into fast hydraulic servos, which you no longer need for anything smaller than a horse. Gyros and accelerometers are cheap now, because they're phone parts. Motors and motor controllers are much better and cheaper now. Big Dog's compute power was a Pentium 4, which is nothing today. Force feedback sensors for the feet are still expensive, because there's no mass market. You need those for slip control.
[1] https://www.walmart.com/ip/Wind-Up-Wooly-Walker/194850858