While I can see the argument that TEs are big token sales drivers, I can't help but toss in an addendum to the end: "TEs are big sales drivers *among people who are willing to drop $250 or more at a time on TD". I obviously don't know sales numbers, but I would guess that is a very small minority of players. Frankly, I'd go so far as to argue that having a non-stacking +2 transmute would actively incentivize token sales and that the lack of one might actually cause some people to buy fewer tokens as a result (I know for a fact that it can cause fewer token sales, which I'll get to in a few paragraphs).
I can summarize the main problem in one anecdote from my first TD run. So, while we're all sitting around waiting to learn what the heck we're supposed to be doing in the training room, the one other person who has played TD before is explaining a few things and showing us some tokens. Among these is a cloak of many pockets, the first TE item I have seen and my introduction to the idea of TEs in general. The way it was described to me at the time was: "This is the best item you can get for getting more loot at the end because it is only a few bucks, while everything else is ridiculously overpriced and not worth buying." I think that pretty much summarizes the problem- you start at $3-$5 at a secondary market for +1 non-stacking and the only step up from that is the leap to $250 for a PyP +2 treasure with no reasonable middle-ground for people who would otherwise be willing to buy more packs but aren't willing to make that dramatic of a plunge.
So, for another anecdote: when my group and I first found out about crafting one of the first things we did after getting a list of crafting recipes was, ironically enough, look for the exact sort of recipe being proposed- something that upgraded the +1 non-stacking into a +2 non-stacking (I had very quickly acquired several cloak of many pockets to pass around the group and was interested in seeing if there was a reasonably-priced upgrade I could do in the meantime). In fact, it was at the point where we were proposing all going in on a $250 bundle in order to have enough tokens to do some basic crafting. Ultimately, we did find our craftable TE, but when that ended up being the CoA and nothing intermediate existed that plan fell apart. So, what started as a group of six people all willing to pool together ~$40 towards buying tokens from TD ended up being $5 at a secondary market for cloaks and calling it a day.
...And that wouldn't have even stopped me from going after to IS TEs, even if said intermediate had eixsted. After all, +2 non-stacking is very clearly strictly worse than unrestricted +2 (I mean, if they printed a +2 strength charm that doesn't stack with any other strength bonuses is it going to kill all demand for a greater onyx charm?). Rather than remove incentive to make big orders later down the line, it would have just prompted me to spend more on tokens to be able to get more treasure right then and there while I worked on building up my strictly better collection of TEs. The way it stands now, I barely know anyone who plays TD but can still name seven people who were dissuaded from buying more tokens because there was no middle ground between the +1 non-stacking and the +2 IS TE.
At any rate, while I won't pretend to be great at math or to have any sort of deep knowledge over any financial numbers involving TD, I do have a few observations to bring up:
1) Over 8000 people participated in TD at this most recent Gencon.
2) Among all the people who have played TD over the years, fewer than 1000 have shown up to post more than twice on the forums.
3) If literally every one of those 1000 showed up to Gencon and only the remaining ~7000 were somehow convinced to buy a single token pack more, that would be another ~$56000 just from small-time purchases.
I think it is safe to say that the casual crowd greatly dwarfs the crowd of truly dedicated players, so things that convince them to buy even a few token packs they otherwise would not have are a pretty substantial source of revenue. Hell, that's if you could only persuade them to buy a single extra pack, much less drop ~$40 pooled together like my group had talked about. So sure, keep printing IS TEs that stack for the dedicated players to vacuum up, but also throw a strictly worse alternative to the casual majority that is turned off by the $250 barrier who would be more than happy to throw a bunch more money at TD for said strictly worse alternative.
TL;DR: +2 non-stacking craftable TEs are great and would likely incentivize more token sales from the casual majority of players.