Now that RC10 is on Steam I think it would be best for IPACS to stop selling RC8 on Steam and provide a free, or discounted price, for RC8 Steam users to upgrade to RC10. RC9 never actually came to Steam btw. Continuing to sell RC8 (for about the same price) is kinda silly imho.
I know that the previous response from the developer was that they could not do this, but I don't think that this is the case. Realflight did the same with RF9.5s and their newer version Realflight Evolution. Those that actually bought RF9.5s on Steam were given a free upgrade to Evolution. At the same time, Realflight stopped selling RF9.5s on Steam. Those of us, like myself, that already got a free Steam key to upgrade our Horizon Hobbies RF9.5 to Steam RF9.5s were given a 40% discount (probably should have been more imho), and this still is the case. This still allows RF9.5s users to continue to use both sims. So, this would also allow Steam RF8 users to continue to use this as well. Obviously, neither older versions will get updates, unless they are security related.
Personally, I prefer to buy apps on Steam because it makes it easier to transfer onto new PC's by just using your current Steam account. I already have IPACS downloaded versions for both RC8 and RC9. I also bought RC8, plus both their DLC's, on Steam so I could use it on multiple PC's (one at a time of course). Anyway, just my $0.02 worth.