Even with 10% taxes (Highsec niveau) it will very likely take a huge amount of time to get the investment from the POCO on non P4's back. And once the taxes raise beyond the 10% mark highsec gets a lot more attractive, at least for finishing P4 goods.
This is the main problem. With current P4 taxes, it actually doesn't take THAT long to make back a single POCO (full P4 production of one pilot about 6 days I think, but few people do full P4 production in low-sec, and usually you can get more than one pilot; so make it a month maybe, that's quite a good RoI). Making back the money for multiple POCOs takes proportionally longer.
CCP needs to fix P1/P2 values for the taxes. They most likely will. The problem here is to make it attractive enough to get some groups to live in low-sec, but not attractive enough to make 0.0 alliances feel interested.
POCOs are roughly on the level of small towers to take down, by the way. And small tower defenses aren't really worth mentioning, either. I suspect there will be a big wave of POCO attacks initially because they're new, but it will quiet down quite a bit later on, with POCOs in backwater low-sec systems pretty safe and POCOs in pirate home systems regularly taken down.
With some luck, CCP's hope will happen that those pirates actually set up POCOs with sensible tax rates. But who knows. :-)