Are you sure? ISTM that it would initially prefer either electrons or protons, and when it had swallowed a couple of them it would repell any more. (Electrons are smaller, so it might prefer them, but they are also more uncertain as to their position, so it might prefer a proton.)
So say it swallowed an iron nucleus. This would give it a strong positive charge, so it would repell any additional nucleus. The question is could it also swallow electrons, or would they go into orbit around it?
*My* guess says that it would need to be sufficiently larger that gravitational effects would dominate over electromagnetic effects. OTOH, since 6 picometers is around 1000 times the size of an iron nucleus perhaps I'm overestimating the problem. That said, what's going to slow it down? This is an accelerator, so even if it created something with the mass of Mt. Everest, it wouldn't be at rest, and would, in fact, be moving far above escape velocity.