@Walter, when you do this modification, what are your plans for the frame and build plate sizes?
With the Y-rail relocations, that X beam would have a longer span, and it also forces you to use a longer span for the bed carrier on the Z-axis. Not critical problems by any means, but it does give more opportunities for bending/warping/twisting.
I've thought about this too with my FT-5 plans. As designed, the FT-5 needed a larger footprint for the Y-axis, as the steppers needed to fit past the rails on one side, and the idler pulleys past the rails on the other. The linear rails themselves are what, 400mm long? So everything is conservatively large for the 300x300mm build plate.
It seems to me, that with some clever positioning of the motion components (like you have done), a 400x400mm build plate is a very real possibility. Likewise, you could build what is effectively an 80%-scale FT-5, and still retain the 300x300mm build area, but gain some rigidity (and reduce moving weight) from reducing the spans.
Of course, that's the point where I told myself I was no longer modifying a FT-5, but in fact building a different printer.