Let's see....
I have the Steam version of TRS2019. Was I ever able to beta test this service pack? To the best of my knowledge the answer is no. So I should blindly trust your internal testers? As you know Steam only allows one install per PC. So I can't have multiple versions as with the retail version.
If you look at my timeline you see that I have pretty much bought every version you have made over the years. Better still check my serial numbers and you will see that I often bought more than one copy of a version. Most of the time I have had both the retail version and the Steam version. Now we both know that each new version of Trainz is not 100% new code. Improvements represent maybe 30 to 40% yet I get to pay for the old code all over again. Under the old business model you had to be sure that the 30 to 40% new code was exciting enough to entice me to buy the new version. Under the subscriber model that pressure is relaxed or at least that has been my experience with every subscriber plan for software I have used. Now I know that TANE was different in that it was a full rewrite from top to bottom and it shows in a much improved product compared to TS12. Under that model I often skipped versions of productivity software because the cost wasn't worth what I would get. This was quite common among users of Adobe software. I owned Photoshop 2.5, 4, 6, 7, CS2, CS4, CS6 before they went to a subscription service. But with a 18 month development cycle users skipping versions is a big problem. So enter the subscription business model where I pay $20 per month to have access to PS and Lightroom plus 1TB of online storage. And like your subscription plan, if I stop paying the software stops working. Hence, my current interest in finding replacement products for those programs. (Luminar 4 is an amazing program BTW.)
See my real problem is with that last bit. You quit paying and it quits working. I'm a sucker for new features. Send me an email outlining the new features of a piece of software I own and bang, you have a sale. But tell me I have to pay this month just to keep the same stuff I have working and we have a problem. It just feels like I am paying for nothing.
So my advice is consider different subscription models. Here are some used by other software I have.
Magix - They handle sales and support for several software developers like Xara. You buy new software and you get the update service contract included. This gets you updates including new features for a year. You can renew for another year for 80% of the original price. You also have access to online features like more templates, images, web widgets and more as part of the contract. If you don't renew then your software continues to work but no more updates and you lose access to the online features.
Techsmith - Makers of Camtasia and SnagIt. They have a yearly cycle of new releases but they offer Camtasia to new users for $249 and updates for $99 to existing users. They offer a Maintenance plan of $49 per year when you update to a new version so you not only get the new version now but for $149 you get the next major release when it is available. They also offer access to an online collection of graphics, music, animations and more for a monthly fee.
E-on Software - Makers of Vue landscape rendering software. This is more of an installment plan. Divide the cost of a new future version into monthly payments of $12 per month for 12 months. Then you get the new version when released. They also offered in program purchases of 3D models, textures and training material.
If your subscription plan was like any of these three I would jump on it but the "pay or it stops working" is a nonstarter for me.
And lastly, before I retired I was an engineer for a small ISP where I would be in the data center at 4 a.m. 7 days a week and would work 14 hour days. Plus be on call 24/7 365 so I know about hard work.
William