There's been rumours of a new Transalp for ages, and it's an obvious gap. The problem for Honda is they don't have an existing motor to fit it, with nothing new coming between the 500 used in the Rebel/CB lineup and the 1100 used the the big TA/Rebel/CB line. There's the 650 used in the CBR, but an i4 doesn't make much sense on the ADV side.
As everyone is doing these days, I'm sure if they do up a midsize motor, it'll end up in at least two other bikes. My assumption for Honda is they'll go bigger than the <700cc motors that Yamaha and Aprilia are using as that would be too close to the existing 500 platform. It'll probably be closer to KTM's 790 range, or at least that's my guess.
Either way, it'll be interesting to see how they differentiate. The Africa Twin is way lighter and more off-road capable than most of the supersized ADV options, but the middleweight competition is much more oriented that way already. Maybe they reverse course and make a plusher 800cc distance bike with vague off-road ambitions?