Wouldn't the six voters have to wait until the outcome of the trial before they could do that? Or are they just anticipating that he will be found guilty and commencing action now?

Ok, from that article I can see that they are basing their action on this:

"The group included findings on Trump's efforts to overturn the election results that were revealed by the House Jan. 6 committee, which dissolved in January after having concluded a lengthy investigation into the riot, as well as from special counsel Jack Smith's investigation that led to one of the four criminal indictments against the former president."

I guess there is time pressure to start their action now, given the impending election processes.