NSEU - thanks for the reply. There's some very interesting and helpful stuff there.
With respect to the number of motors and complexity - I only propose to use one motor per seat, so if you want to recline, you will also have to accept the leg cushion coming out too (and another important dynamic change that I can't mention at present). This might seem stingy, but it allows the mechanism to be infinitely more simple and the whole structure to be lighter.
I believe the great increase in comfort over standard economy seats will offset the limited control over body position (in comparison to a business type seat)
With respect to access for maintenance - I had considered using a quick-release subframe carrying the motor and main mechanicals that can just be swapped out with another, but that would increase the weight quite a bit, and also be cumbersome, especially servicing a window seat on a 3 abreast layout.
Access to the motor and associated parts would be by removing the seat bottom, as you suggest. Since the lifejacket is contained within the leg rest/foot rest this is easier to achieve.