What exactly do you mean by mainstream? If you mean accepted by the general population, then I'm guessing not. In fact, as a random individual, I know nothing appsumo AND reddit (I didn't even know appsumo existed until you said they did so in this blog post), so if those things are not mainstream, then I highly doubt "death-is-bad" would become somehow become mainstream by associating with non-mainstream stuff.
I meant "random company wanting to make a deal that would appeal to the overall reddit demographic ended up selecting SENS as a charity that it thought would appeal to them."
Reddit may not be "random person on the street", but it's more mainstream than, say, LW or your favorite transhumanist group. So it's interesting that a company trying to appeal to reddit overall decided that SENS would be the organization of choice to donate some of the profits to.
So, apparently appsumo is having a custom reddit bundle, a bundle meant to appeal to redditors, and 10% of the proceeds get donated. On the surface, doesn't sound _that_ interesting, except...
Take a closer look: http://appsumo.com/reddit-special-deal/ and find that the recipient of the donations will be... SENS!
I find this to be an interesting development. It wasn't the "custom transhumanist bundle" or "the custom sens bundle" but "the custom reddit bundle". Yes, "reddit" doesn't, in and of itself, count as extremely mainstream as such, but I'd say it's still an interesting development.