I see some players are still trying to hang on to the old options.
I think opening race unlocks for full tiers in a pre tree opens up hundreds to thousands of effective design choices for multiclass characters depending on what becomes available with helf and human that would be impossible otherwise.
A concern I would be having with adding more windows is that since we provide all these options for the multiclassing without enforcing making the choice through the tree limitation players are going to ignore most of those choice regardless with there best list from all the trees and homogenize choices again. Just browse the builds on the forums and a person can see that the all take pretty much the same enhancements in those multiclass builds.
The limited tree selection enforces more build diversity while providing a lot of choices instead of just "here is everything check out such and such a thread so you know which works best together because the other choices are meaningless because you have no AP to spend on them anyway".
Opening up all the trees does not open up all the choices. It opens up making master lists of the best choices and ignoring everything else.
The other concern is that if we were to allow all of the enhancement options available and helf or human provide a large variety of racial PrE unlocks there there is little to no incentive to make a pure class outside of an offensive caster who needs the caster levels for damage or spell penetration, maybe another slot. Even then a splash will often provide more benefit since the capstone is readily available without going pure class.
Posters keep saying the new system is not multiclass friendly but it looks incredibly multiclass friendly. What is doesn't look is pure class friendly opening up too many options for multiclassed character.
I would much rather see a few old builds need to be reworked or stop working in order to open up the diversity available on multiclasses with the higher tiers of enhancement options the new system appears to provide than to see options opening up to the point that it impacts the playability of pure classed characters.