...some kind of ranking system that ranks you in terms of speed and volume of contact while racing and then the ability to filter your open lobbies to include or exclude certain levels of drivers. New drivers, if they choose, should be able to exclude guys that are much faster than them and vice versa.
Good luck implementing any sort of system that keeps track of contact, since it'd be very hard to sort through whose fault it was. Would you enjoy your record getting worse because somebody in a random lobby decided to go on a ramming spree in an X1?
As for the latter suggestion; an interesting one, and I can totally see the reasoning behind it, but I could see problems, especially if PD gave us the ability to "reset" our status, similar to some fighting games' win/loss ratios. I can't tell you how many times I've run into "amateur" fighting lobbies to find people pulling off ridiculous, masterful combos

.
1) No. GT5 is supposed to be a realistic driving simulator. Swapping engines is a Forza thing.
I think you meant "real-life thing", seeing as how
even manufacturers do it. It's incredibly common in the lower levels of racing, and gives us so many more options, including re-creating more accurate replicas of cars PD may not have included. Given a thoroughly in-depth system with Audi or BMW, for example, you could recreate a massive chunk of their lineup much more realistically than relying on the (broken) engine limiter feature we currently have.
2) No. As some have said, power really isn't everything. This would just attract yobs who can't spell and know bugger all about cars to go online and compare their ridiculous power figures with other people in pathetic little Civics. I fear this would ruin the online experience for people who like GT5 to be a proper simulator.
So arbitrary power limits, decided on by the game's creators, should be taken as the only right limits?
We already have ways of limiting our dealings with the unwashed, awful-driving masses in GT5. With access to the right limitation options for rooms, it would be just as easy to keep them out.
3) No. Special Stage Route X is perfect for drag racing, and as for drifting, surely it's better to create your own tracks and keep them to drift lobbies only.
Except we don't get to create tracks; the game spits some out based on a handful of vague choices we get to make. If we had a proper track creator (and I'm not even asking for one, because to do one properly to the realistic level of GT would be an utter headache for PD), sure. But I wouldn't say no to them creating one or two purpose-built drag circuts or point-to-points; it's a big bit of automobile culture, especially in Japan.
I completely agree. I just think he was worried that people would demand to put unrealistic engines in cars, engines that are way too big or powerful for the chassis. As long as it was handled sensibly I'd be on board.
Let someone put a gigantic engine into their front-drive hatch though, and let them struggle with the awful nose-heavy nature of it

. (My thoughts again with the next quote).
This is what I meant. People would put big engines with several hundred brake horsepower into little hatchbacks. Te fact of the matter is that the engine bay of each car is suited to its own engine. Also, engine swapping isn't as common as some people make out.
If the engine bay of each car is suited to its own engine, than how come there are multiple different engines for the majority of cars out there? The Mercedes C-Class, for example, ranges from a tiny 1.8L all the way to the big ole' 6.2L V8. Aston's tiny little Toyota-borrowed Cygnet can even fit the company's V8.
Implementing engine swaps wouldn't be easy, I'll admit; we probably shouldn't be able to drop something like a Viper V10 into a Dart, or something silly like that, so there do need to be reasonable, logical limitations, which would require some research on PD's side. But nearly
any engine can fit into nearly
any chassis with the right work and forethought. For an example, FM4 does it fairly well, usually limiting transverse to transverse swaps, and longitudinal to longitudinal (with a few exceptions). Horizon then threw this away with a simplified, unrealistic approach, though 👎.
PD would only need one more detail from manufacturers; the engine weight. Letting that fluctuate to more accurately represent the swap, and also affecting the front/rear balance, would be great. Throw in the fact we have the PP system (which isn't perfect, but at least works as a rough yardstick), and engine swaps would just provide us with another, different approach to tuning 👍
...
Lastly, to the OP; seeing as how it's unlikely we'll be getting any major revisions to GT5 at this point, you may want to list your suggestions in the catch-all thread for GT6 ideas (that aren't cars or tracks)
located here.