Probation is a non-starter, it's not even on the table.
However, type ratings might be undecided for right now. There are most likely discussions of that ongoing and it remains to be seen what will be done with that. It's a pretty hefty financial chunk of change, our 737 F/O's aren't typed (unless they were typed somewhere else) and of course anyone wanting to transition to the 737 would have to be typed. Normally I'd say that Southwest would have to pay for that, but Southwest isn't a typical airline.
The sticky part will be how you deal with current 737 F/O's. How do you force someone to go buy training when they already have the job and neither CBA allows for a pilot to be terminated or displaced because of a type rating purchase. I imagine you'd wind up with a DFR lawsuit against ALPA by our F/O's pretty quickly if they deliberately negotiated away a $7k or $8k chunk of change from their pockets.
The only way I can see around that is if the ARBITRATOR includes it in his decision, and I highly doubt anyone would, as it's not germaine to a SLI decision. But as far as the 717 pilots who transition over at a later date... if it's not because of a displacement... you never know.
Just food for thought.