Yes -- This is one of the open questions for discussion, and one of the most important. (HotPETS is a "workshop", which in Academia is the precursor to a conference... papers are meant to be early stage drafts ready for discussion. So we are curious how people would be interested in the currency.)
You're right, one of the early reasons for purchasing TorCoins would likely be donating to Tor. But they are a totally usable altcoin, just like Dogecoin for example. What reason do people have to buy Dogecoin? Not much, beyond using it as a currency or speculating with it as an investment. I could see TorCoin working the same way.
Another use you should consider is to follow the FON model - you can spend TorCoins to buy bandwidth from people operating networks.
The more bandwidth you share for TOR, the more free wifi you get.
If you only "sell" wifi to torcoin owners, you simply trade internet access time, but running a tor relay would be like "mining" in the traditional bitcoin world.
EDIT: The point I'm trying to make is that instead of "just" the way to create torcoins, this would also create a way to spend it (and provide value to people by spending it).
Dogecoin is an example of excellent and deliberate marketing.
From branding decisions ("Let's stop people talking about us as the joke coin, and start people talking about us as the community coin") to PR (Constantly reaching out to big news outlets, carrying out small-to-medium PR campaigns) to content marketing (the tools available for Dogecoin have quickly grown in number and sophistication - check out moolah.io for instance, which began on /r/dogecoin) to incentive marketing (they're constantly giving people small stakes in Dogecoin's success).
Quite frankly, it's weird. I think of Dogecoin as the marketing coin now, which is most of the reason I've withdrawn from the community somewhat. I really don't want my day job getting mixed up with my free time.
> What reason do people have to buy Dogecoin?
No technical, practical reason. But you may find that without that consistent, sustained marketing that people won't use your coin so much.
You're right, one of the early reasons for purchasing TorCoins would likely be donating to Tor. But they are a totally usable altcoin, just like Dogecoin for example. What reason do people have to buy Dogecoin? Not much, beyond using it as a currency or speculating with it as an investment. I could see TorCoin working the same way.