Yes, replayability is one of the things I'm looking at now.
I want to keep the core loop simple, satisying and endless rather than add lots of changing objectives. Block Blast is one reference for that rhythm: mostly stable rules, with occasional situations that force you to think more carefully.
For Lex Blast, I'm experimenting with periodic challenge rounds, for example starting from a single central anchor and a more constrained rack, to create those moments of extra tension without changing the core game.
Do not hesitate if you have ideas or recommendations.