My only worry here, as a user of both services, is that I use Flickr as the place to dump a LOT of photos all at once. It’s my library of photos. I use Instagram for those few shots that are worthy of sharing RIGHT NOW.
Even with the grouping that the Flickr app does on my iPhone, I’m not sure it’ll be a good experience for keeping up with everyone’s photos, especially when we all do the occasional post-vacation or family event bulk upload.
Or, maybe it’ll be like Facebook and everyone will be OK with the volume/trusting the feed algorithm. I’m not confident about that, though – there’s a reason I choose Instagram over Facebook. Selectivity & signal-to-noise matter to me.