I would start up my old 360 just to get Forza 2 completed. But the servers that would need to be run in order to accomplish what y’all are suggesting would run costs up crazy. Because as soon as word gets out “Forza 2 servers are back up”, then a whole bunch of other people will rush into it to get the extra points for their Forza Score (assuming there is a decent mass of people that care about their Forza Score to begin with).
I started on Forza 2 and I miss all of the old supercars that were either replaced with a newer version in a later game or completely deprecated for reasons I don’t know. Same thing with the original Horizon. The Joss JT1, Ascari, etc. I’m glad to see the R390 in Horizon 3, but I hardly see any of the old supercars present in Forza 2 make it to anything past Forza 3. The Koenigsegg CCGT and CC8S were my favorite hypercars from Forza 2 (iirc they were both in it). Now all we have is the Agera, One:1, and Regera. Not even a CCX-R anymore.
Although we did get Porsche as well as NASCAR in Forza 6, most of the more abstract and less-known supercars have not made their way into later releases. Licensing is a big issue, indeed. Which is what most everyone thought was the reason for Horizon’s delayed release for Xbox One backwards compatibility.
All in all, it’s not logical to open up servers for just one achievement. Yes, I am somewhat of a perfectionist, but 19990 is high compared to the majority of casual Forza racers. That 10G will get you to 20k, but would it be worth the time and effort for the dev team to set up servers with the (possibly) outdated technology to run the servers? I think not. I will donate if the petition gets a decent turnout, though.