What would happen if the number of memorial partakers rose to more than 144,000??
Nothing major. It's already obvious that there has to have been more than 144,000 partaking over the history of the WTS let alone those first century Christians. The majority just follow the rhetoric.
I expect that we shall see WTS address rising numbers with yet more nonsense about the figure being unimportant, reminders it's only the GB that are the F&DS and for some strong articles about how unhappy Jehovah is if you partake without being 100% certain. They will probably make some statements about the depth of spirituality (i.e. stuff you do in the org) that a member of the remnant would likely have to try and guilt some into retracting their claim.