If you have a Ferrari that can go +300km/h, and add an engine from a Lamborghini, that can go also +300km/h, new cars engine wont go +600km/h. Same is with Renault, if you add engine parts from Renault Clio to Ferrari, it wont do same +300km/h.
Moving trading volume from alts to Bitcoin, for example, will cause a price growth in the beginning, as Bitcoin owners will try to sell their crypto more expensive, but later the price would go down and normalize. It will be sort of a pump and dump, but without hitting bottom.
I would not guess that it would go back to what it is right now, the amount of people who sell will not be as big as the people who buy. The market cap of the whole crypto world would drop, and significantly as well, but the marketcap of bitcoin would be so much higher.
There will be like a trillion that go in, and even if like half of that is gone, the other half would still be there and the price would skyrocket for sure. We will have like 500k per bitcoin price, but the total would be lower than the total crypto marketcap of right now. This is why I do not feel like it means anything, it doesn't really mean anything at all if you ask me and shouldn't even be considered a good idea. Not like it can be done anyway.