The Steem blocks themselves -- without any index data -- are well over 3GB already, and will only continue to grow. Since 32-bit machines are limited to 4GB of address space per process, this means any database implementation would be impossible to implement on a 32-bit machine unless it either does (a) or (b):

• (a) Processes the blockchain in a way that throws away most of history
• (b) Keeps its data and indexes outside the memory address space of a single process