As far as I know, even a successful test of quantum immortality involves greatly thinning out the number of timelines in which one exists, which is an extremely high price to pay for learning it. The cost of trying out a MWI-based lottery, even if it fails, can be relatively small. There seems to be more than enough difference to be willing to test the latter but not the former.
As far as I know, even a successful test of quantum immortality
Presumably you mean a thought experiment, not an actual test.
The cost of trying out a MWI-based lottery, even if it fails,
How would you know if it succeeded or failed?
I haven't been able to find the source of the idea, but I've recently been reminded of:
This is, of course, based on the Multiple Worlds Interpretation: if the lottery has one-in-a-million odds, then for every million timelines in which you buy a lottery ticket, in one timeline you'll win it. There's a certain amount of friction - it's not a perfect wealth transfer - based on the lottery's odds. But, looked at from this perspective, the question of "should I buy a lottery ticket?" seems like it might be slightly more complicated than "it's a tax on idiots".
But I'm reminded of my current .sig: "Then again, I could be wrong." And even if this is, in fact, a valid viewpoint, it brings up further questions, such as: how can the friction be minimized, and the efficiency of the transfer be maximized? Does deliberately introducing randomness at any point in the process ensure that at least some of your MWI-selves gain a benefit, as opposed to buying a ticket after the numbers have been chosen but before they've been revealed?
How interesting can this idea be made to be?