Instead of adding support for altcoins they should spend some effort into advertising Bitcoin, and onboarding people who do not have a bitcoin wallet yet. Thats how you expand imo.

Adding altcoin support is not really gaining you new users, since altcoiners probably hold BTC anyway or could easily swap to it to use your service if they wanted to use it. I dont know if that makes sense. Supporting multiple blockchains will not grow your business getting people outside of crypto set up with a Bitcoin wallet will.