Isn't there a Google PageRank penalty for sites that do that now?
https://developers.google.com/web/fundamentals/app-install-b...
It uses some heuristics:
> Be visited by the user twice, over two separate days during the course of two weeks.
I think apps installed this way should be also limited to some subset of permissions they can request[1]. Otherwise this is almost like a bookmarking mechanism.
[1] They could still explicitly ask for more, on use.