There are still several factors that need to be developed in BTC. Two things that come into my mind is its integration to real life activities and its confirmation time. Yeah, I know that BTC is already being integrated in several countries/cities in the world but what I meant here is we still massive adoption and integration of it to the large part of our population. I noticed that as more people started using BTC, the confirmation time it takes also increased. This comes hand in hand and the devs should find the solution for this. Confirmations time for BTC should be fast if we wanted it to be used in our daily lives. These two points should be prioritized the most in terms of BTC development.