There isn't currently a way to detect pen pressure, (it's a bit difficult portability-wise) but it is possible to define custom brushes that respond to the speed or direction of strokes- see the "brushes.deck" example deck.
Lil was designed and written for Decker; the platform and the scripting language co-evolved. There's no deliberate influence from Smalltalk; Lil is primarily aesthetically influenced by Lua (which is popular for beginners) and semantically influenced by Q (which contains many powerful ideas, especially its vector-oriented and database-related functionality). I have a background working with APL-family languages, and Lil is an attempt to surface some of the same expressiveness and design philosophy in a more approachable package.