The first problem is not specific to Scrapy; it is the same if you're using inlineCallbacks from twisted, tornado.gen or async def: there is no way to serialize tasks inside coroutine and save them to disk, e.g. to be able to stop the process and then restart it from the same point, or to avoid keeping the whole request queue in memory.

Stream processing could fix the second problem, but it is not a practical solution: in most cases one needs to build HTML tree in memory to do further processing (e.g. extract links). I'm also not aware of streaming regex libraries.