Short answer is yes I think it will go mainstream.

Now, the longer answer is I don't think the bitcoin practiced by bitcoiners now will be mainstream. It will be more common but I think plenty of people will use custodians and opt for convenience over sovereignty. Why? Because people are slow to learn lessons. Now, if we have a really rough time where people lose everything and they learn the value of sovereignty and risk of trusted 3rd parties then that might change. The bottom line for me is it doesn't matter. What does matter is that we have to ability to save our life force in an incorruptible medium that we can sovereignly hold. There will always be foolish and lazy people. Don't be one of them.

Edit: Actually, I often wonder how many "bitcoiners" actually hold their own keys. There are a lot of phonies out there. Talk a big game.