This would mean you won't find your older rolling stock on newly bought routes, as previously bought rolling stock will not be able to be layered in. So expect a complete do-over ,just like when TSW first launched, with mostly empty yards and not much variety in rolling stock. It would take years, not to mention a lot of money from the player's end to rebuy everything, until the UE5 based sim would be up to TSW's current level. You CAN convert UE4 models and maps to UE5, but it's not a "Save as..." type of action. There is significant work involved, and that's even without adding any new UE5 features to your maps or objects. If you plan to do that, it's even more work. It's not realistic to expect DTG to do that, and then give you those converted routes and rolling stock for free. A rebuy/upgrade pricing could work, but I can already see the forum threads about bineg ripped off in my head.
Personally, I've never asked for anything for free in my life. If certain "improvements" are the result of hard work, they should be adequately compensated. It's better than being left in uncertainty.
The one thing you never hear on these forums is why people keep asking make it with UE5, what are your reasons? is it just shinier graphics? Because after reading a metric ton on both UE5 and UE4 the main differences i can see are basically lighting, sound and the way it handles open worlds (imo relevant points), so knowing this and also knowing the main bottleneck in TSW is simugraph, what do you think the outcome of TSW moving to UE5 would be? because i can make a pretty educated guess on the outcome.
If there's an alternative to UE5, that's fine. But the most likely scenario is that DTG will stick with Epic's engine, for a "possible" new simulator. This has practically been stated by DTG itself (remember MR? ). But we're in the realm of unofficiality, not official.
Honest opinion based on research says that's a (my opinion before certain folks have there tantrum) massive mistake, even unigine 2 or if there willing asobos flight engine would be a technical better fit, but at the end of the day it'll be more likely epics deep pockets that dictate that not what's best.
