You can never have too many Landsknechts
Basically you can paint them in multi-colours, so no real restrictions on which army they can fight for.
Amongst others, I have metals from Artizan, Foundry, the Warlord Games (Pro Gloria) and like GP some due shortly from a recent Adam Holmes KS.
The ones I have already all match sizewise pretty well, and so I expect the new plastics to fit too.
It will be interesting to see if they are solely Italian or whether there will be bits to make Swiss for example.
I have some Pendraken which are a bit chunky, and not my favourites, but I have 'lost' them in rear ranks.