Accurate Strong Gantry

[JAZZCNC]

And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.

Now your getting what I've been trying to tell you for nearly last 2yrs. . . . . . . It gets even more stupid than just the spindle because half the time these massively over engineeered machines only ever cut wood or foam.!!! CRAZY

This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.

Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!