Super early predictions:
Mercedes - Hamilton/Bottas
On current form there is no way this changes, of course Bottas has plunged in performance the last 2 years as the season goes on so keep an eye on that, but it's unclear what Mercedes benefits from appointing Ocon as it stands.
Ferrari - Vettel/Leclerc
This is already getting uncomfortable, but it's a strong pairing Ferrari will want to keep taking advantage of, if it doesn't blow up.
Red Bull - Verstappen/Albon
The only change I expect on the top teams, Gasly's performance will get him out of the car for sure unless it dramatically improves, and quite incredibly Albon seems to be on pole position for a promotion now. I don't think they'll go for a mid-season change again though, they'll wait for the end of 2019. There's the odd chance Red Bull could hire from outside STR, but with Albon looking promising I think they'll keep true to their tradition.
Renault - Ricciardo/Hulkenberg
No reason to change for anyone, very strong pairing for the team and neither driver has real options to move up from this.
McLaren - Sainz/Norris
Also no reason to change and no better options for either driver.
Racing Point - Stroll/Russell
Stroll's a given, Perez will not want to leave as he'll want to benefit from the investment put into the team which should only start translating into results next year, BUT there's no other place Mercedes can really put Russell to test him.
Haas - Magnussen/Perez
Haas has been very loyal to the current pair of drivers, but with the likes of Perez and potentially even Ocon in the market, it might be time to gamble getting rid of Romain to see if it results in an upgrade.
Toro Rosso - Kvyat/Ticktum
This is a tricky one because I think any combination of Kvyat, Gasly, Ticktum, Vips or even Auer is possible, and that's already under the big assumption Albon gets the promotion. I reckon this is the likeliest combo tho, proven measuring stick (which I suspect brings some cash) agains the erratic, temperamental, but ultimately most promising quick kid. Would be very harsh on Gasly to completely drop out of the grid though.
Alfa Romeo - Raikkonen/Ghiotto
Kimi's on a 2 year deal, the problem is the other seat, Gio's been very disappointing tbh, and I seriously doubt Mick's ready for the step-up. Bringing in another Italian who I expect will do well in F2 this year, might be a logical stop-gap.
Williams - Latifi/Sette Camara
I expect Williams to completely plunge into the paydriver route 100%, as Kubica seems unhappy and not performing, whilst Mercedes will want a more meaningful test of Russell's capabilities. Latifi's already within the team, whereas there's always pressure for F1 to get a Brazilian into the grid as that's a big market - perhaps Sette Camara or Fittipaldi the grandson could aim at this final seat?