The default is already unlimited and that IS a problem for people. There is a reason the old setting is still being used by nodes.
The way I described it it still limits the number of transfers. But I guess it would be possible to store piece sizes as well and pivot that to an actual bandwidth limitation. However, I think transfers have a random write overhead due to database updates as well. So I could see advantages to either option. I didn’t even think of the fact that this could also open the door to nodes with bandwidth caps.
I recommend you take a look inside those db files and see what they are for. But here are some hints; keeping track of used serials so uplinks can’t keep downloading your data, without you getting paid. All the stats on the dashboard. When pieces expire and your node can remove them. etc etc. These aren’t things that can be done without keeping track of some data.