Saying '8' is slightly ambiguous here, he's already playing the role of 'our most advanced' midfielder pretty well, and at times very well, this season (whatever the general perception on here which has often been wildly wrong)
Our RCM is very often our most advanced midfielder of the 3 (depending on personnel) .. mostly because we want Salah and Trent a bit higher than their left sided counter parts ... in our classic somewhat flat midfield 3 Henderson was often higher up the pitch than Wijnaldam.
This season Harvey's one of the leading pressers per 90 in the league (he's in the top 5 possession adjusted)
His tackle plus interception number this season is 2.14 ... last season Henderson's was 2.04 (and Henderson pressed a lot less)
There's no doubt he can be our most advanced midfielder effectively in a 3, he already is at 19. It's mental to me that people can watch last week's game at Anfield and not think this
My concern, and maybe I'm not understanding the way we play here, is that pressing and tackling doesn't tell the full story. When we're in the ascendancy then pressing high and winning the ball is great for creating chances and protecting the defence, but when teams break past the midfield or are pinning us back, midfielders need to be disciplined, track runners, fill gaps, and help keep us solid until we can gain control and impose our football on the opposition again. Elliot is great at pressing high when the game is going our way, but when we need to dig in he's (on camera) literally nowhere to be seen.
I must be wrong about something because I find it kind of baffling that Klopp doesn't seem to care about this. Back when Keita got hauled off at half time on a couple of occasions my assumption was that this was the exact issue, he was great at the high press but not so great at the tactical discpline side of things, yet Elliot gets a free pass. Maybe someone else is supposed to be helping Trent, maybe we want him to stay high and expect our other midfielders to shift across to fill the gap, but whatever the plan is it doesn't seem to be working.