In terms of the geometry of the bike going to 27.5+ will keep the diameter approximately the same as a 29" front wheel so you should be equivalent there assuming the forks have the same crown to axle length.
It will give the front wheel extra suspension through the flex of the tyre. I don't know your setup so I can't comment specifically but if you make the front end too plush you may find the rear end can't keep up with the front end. You don't want to add expense, add the extra weight to the front end and not get much back for it. What exactly are you trying to solve with the upgrade?
Can you fit 29+ up front instead?
That will change the geometry to be slacker on the front end. Not necessarily a problem but 27.5+ will keep the geometry closer to what it is currently.
Personally I think that bikes should have kept the 559mm (26") rim size and just made larger tyres/ wider rims to suit. I bet a ~559-60 tyre rides much the same as a 622-53 tyre. What you lose in in diameter you make up with the extra tyre deformation over obstacles. Really there is only an 11% difference between a 26"/559 rim and a 29"/622 rim. The actual diameters don't mean all that much for rolling over obstacles but the 26" wheel is easier to design a frame around, especially if you want a short rear end. Why there needed to be a middle standard size is beyond me. Of course there are great bikes of all sizes. I ride a 29" and think there are 27.5+ bikes that look like a lot of fun that would suit me well.
