Yes, a lot of places are looking at faster boarding. Proof of payment or prepaid tickets are one approach. Some systems have semi-sealed bus shelters where you pay to get into the bus shelter and then the bus pulls up to it and you walk on.

Carpool lanes could work but in fact in some places they are filling up. On city streets, carpool lanes are harder. If it's the inner lane, it's fast but you have to figure out something for left turners -- or give up left turns. If it's the right lane then people still enter/exit through it, and it's slower, and cheating is rampant. You need a system which is fast and cheating is not rampant.