This is exactly what they promise with Alibre xpress.
Large assemblies can be opened in Xpress but they cannot be edited or saved unless they have fewer than 25 different parts (first 100,000) or 5 (current free version).
There is no limit of individual part complexity but I'm not sure what happens if your part uses advanced modelling like shells and the xpress version doesn't have shells (only the first 100,000 had it). Probably they wont be able to edit that part or at least that feature in that part.