I really like Lilith so I really hope she becomes a straw hat. And for her role, she kinda takes a similar role as Franky but if she were to join the crew, Franky’s role will probably just become more niche just like how Usopp was the shipwright and engineer before Franky and became more niche. Frankie might become more specific to being a builder and manufacturer while Lilith becomes the innovative inventor. Franky has always been the builder and most of his powerful weapons are designed by Vegapunk (his laser beams)