Hi psiron
Not sure I understand the how the y axis will work the same.

The obvious problem I can see is that it looks like there are only bearings on the top beam and plate arrangement and the belt drive is then down a lot lower. if this is the case then you will have problems with the bearings binding due to the lever arm (cantilever) effect. I 'd move the driving part of the belt up to the centre line of the bearings. having the side plates drop down so far will also cause a lever arm in the y axis direction and cause racking that way to.

Another weak point is the belt drive shafts at each end need more support, either a central strap in the middle or the best solution is to support the free ends. it may not be to apparent but once the belts are tensioned and its in motion even the smallest flex will cause problems.

Have you got any more drawings or plans, is that CAD or sketch up? its all good in principle just dosnt look very well executed. to me the whole thing could do with more diagonal bracing, if its done in opposing pairs then they can be considered to act in tension so can be quite small sections with a thin wall.

If it was mine I would turn the x axis bearings through 90 deg, centre it on the plate and then run 2 rails/flat bars for the y axis (1 above and one below the bearing) again with the belt driving half way between the 2, that way it's all braced up with no cantilevers or skewing forces.

Anyway thats my 2 peneth