I think bitcoin will never adopt other new coins because basically bitcoin is made with a limited amount although there are some disadvantages such as the speed that is a bit slow when sending bitcoin but many people we see today are still very interested in bitcoin even though there is a problem of speed when sending not like other coins like xrp which have fast delivery speed but they are not very attractive with xrp coins even though they are superior in the sending system.
Bitcoin is already an established cryptocurrency, there's no need for it to append itself to other cryptocurrency. What is happening is that, other crypto enthusiast are those who are associating their coin to bitcoin, such as the Bitcoin Cash, SV, and much more. In that case, they can benefit from its name to gain fellow supporters and hodlers. When it comes to bitcoin being slow, I don't perceive it could be a problem any more since the lightning network already solved this problem.