It's still an issue. Running at 190 on the gauge doesn't mean it's okay. The gauges are not accurate enough to tell you an exact number (later year capri gauges switched to Cold/Hot, not a numerical readout for this exact reason)
These engines are designed to work at a certain temp.
If the ECU doesn't see that's it's at normal temp, it causes problems.
-You burn more fuel. When the ECU sees the engine is cold(er) it throws in more fuel to richen the mixture, trying to warm the engine up.
-Thermal cycling like Chris said. The fan kicks on at 210 degrees. That means instead of cycling between 195 and 210 degrees (15 degree difference) the engine will now cycle between 180 and 210 degrees (30 degree difference) That might not seem like much, but the head & block expand/contract at different rates (aluminum head, iron block, aluminum expands more) so it causes wear on the headgasket. Not a whole lot. Usually it only sees this from a cold start to warm up, then shut down. But with a colder thermostat you have much wider, more rapid temperature swings, that accelerate wear on the headgasket and other components.
You can get away with it if:
-You tune an aftermarket ECU for a different target temperature
-You change the fan sensor to a corresponding lower temperature
Again, because the engine is made of different metals that expand/contract at different rates - the engineers designed the parts to fit together and work best at one specific temperature and the thermostat's job is to keep it there. Parts will fit different, and wear differently when they are run at a different temperature. (thats why head gaskets blow when these engines overheat, the aluminum expands too much, and the head warps out of shape)
You could run a colder t-stat on an old V8 and get away with it because the fan ran constantly right off the engine, and the tolerances within the engine were drastically different than today's stuff. They were also generally ALL iron (head + block). And stuff got rebuilt a lot more often back then.