Commit e7296bacb2b1981b2991e915daf4b25647224466 refactored BetweenQuery in a way that makes it relatively easy to add support for Expression<Func<TKey>> as leftKey and rightKey arguments; that capability would be useful with complex secondary indexes.
Hm... upon further thought... this isn't going to be very useful. Between with expressions would be equivalent to calculating the bounds client-side anyway. Closing this issue due to lack of use-case.
Commit e7296bacb2b1981b2991e915daf4b25647224466 refactored BetweenQuery in a way that makes it relatively easy to add support for Expression<Func<TKey>> as leftKey and rightKey arguments; that capability would be useful with complex secondary indexes.