Since they're all variants; probably the easiest way to implement them would be along the lines of Archetypes
I.e. add class "Monk", Archetype "Unchained Monk", or something along those lines; It could replace all or any of the appropriate class abilities with others, leaving behind anything that would stay the same
As well, it would still allow other Archetypes to be used (or, alternatively, if others get errata'd to replace [core]A ~or~ [unchained]B, it'd just take a tweak to how archetypes work; potentially along the lines of prereqs)
Of course, we can't really tell until either a playtest or the real deal comes out in a few weeks, but we can always brainstorm
The above is how I'd do it without rewriting the entire character engine
Alternatively, of course, they could be built as new classes, but in that case there'd be reams and reams of already-defined rules/abilities/things that use the core abilities as prereqs, that would all need to be extended to support the potential new abilities