I guess everyone's definition of mainstream is different. But I'll go off the assumption that you mean something like a normal day to day thing people do/engage in. Debit/Credit cards are mainstream for example.

To answer your question I would argue some of the biggest road blocks in no particular order a are volatility, ease of use, safety, and adoption.  When I talk to people who don't have bitcoin and have no interest in it, it's usually one of these things they bring up.  They will point out its too much of a hassle for them (too difficult) , they dont want their money stolen (not safe enough for them), they dont want money that goes down or up constnatly (volatailty) , and there is no were currently that takes bitcoin  (adoption).


Once these roadblocks start getting overcome bitcoin will continue to go mainstream. It's my opinion that all of these roadblocks are solvable and are already steadily being worked on by various start ups and individuals. The only one that people can't really fix through innovation would the volataility issue but I would think/hope that starts to become less of an issue as the market expands.

Have fun with your lecture,  may I ask why you are giving a speech on bitcoin ?