There's also what else comes with these engines. The James deluxe adds milk & tar wagons, his own timetable and 4 James stories. I think each engine carries their own popularity ranking better than others, they all will have an audience and depends on what is offered. If we get one for Fergus and another for Billy, more will get Fergus. Depends what comes with them too, like if you have to get an engine you're not keen on just for a unique rolling stock that's been bundled with them (e.g. Belle with Water Tankers).
Honestly, I completely agree. I’d much rather see 2–3 genuinely substantial DLCs a year than have Dovetail rush content out just to meet a quota. If this really is an in-house project with no third-party teams available to help, then 4–6 months per DLC sounds completely reasonable. But at the same time, they absolutely cannot let it become one DLC a year. After everything we’ve already waited through, that would kill whatever momentum and excitement the game has left. Two solid DLCs a year feels like the bare minimum for keeping the community engaged while still giving the team enough time to deliver quality content.
TSW's expansions come in at £20 to £30 for a route plus a couple of locomotives depending on the length of the route. WoS will almost certainly follow the same pricing model so I wouldn't get your hopes up otherwise. It already has done in terms of the James expansion which matches TSW's single locomotive add ons.
It's true, I would pay to see my classic heros. Because that is why I bought the game in the first place: the first dozen, diesel, boco, daisy, mavis, .... And off course for the main line, thomas his branchline, brendham docks, the sheds, the quarry. That's what is triggering us for months, right???