I like the idea of the paths, however, it might be a tad too complicated for some people. It might make 5e, but not in core, in "splats".
I think it's still a lot easier than hybrids, 3E multiclassing, or dual classing. (The jury is still out whether it's easier than AD&D multiclass)...
All you need is a table:
Level - what you get
1 - ability A
2 - ability B
4 - ability C
6 - ability D
For the secondary path, you just get everything a level later (except the first). It's a bit tricky to design abilities, because you have to make sure they don't create some weird stacking effect. But I think it's dead easy in play. For a basic set, there could be paths where ABCD are fixed, without any choices for the player.
Note that "ability" can be anything - class feature, fixed bonus, feat, 4E-style power (at-will, encounter, daily, utility), spell slot...
The big advantage is that you could have a pure fighter, a fighter/wizard, a wizard/fighter or a pure wizard, and they're reasonably balanced because they progress in the same way.
Note that a Fighter/Wizard is a Fighter (full plate, sword etc) who picks up some spells, while the Wizard/Fighter is a Wizard (robe, spell book) who picks up some combat training.