The 4-2-3-1 seems in vogue at present, and Pochettino is known to favour that formation. The problem is, we'd need a deep-lying playmaker (theoretically) to make it work, and there's a sever shortage of those around at the moment. However, I'd wager we can get by without one if we buy one good player (specifically, Morgan Schneiderlin) and set up like this:
1) Standard set-up: In the 'standard' starting line up, the midfield would ideally look like this:
--------------Bentaleb------------------Schneiderlin---------------
Lamela----------------------Holtby---------------------------Eriksen
Pretty standard 4-2-3-1, with what some would say is a weakness in terms of quickly shuttling the ball from back to front when in possession. However,
2) Transition phase:
------------------Bentaleb--------------Schneiderlin--------------------
Walker--------------------------Holtby----------------------------------Davies
-----------Lamela--------------CF Position 2------------Eriksen-----
OR
---------------------------------CF Position 1----------------------
....this is where Holtby comes in. We know he's a bundle of energy and possesses an ability to spray passes around, with the downside being that he's too positionally inconsistent and drifts towards the action too much. Well, in a system such as this one, the screening midfielders (Bentaleb and Schneiderlin) will be supported by the nominal no.10 Holtby, who in the transition phase will drop deep to pick up the ball from either of the two DMs while the full backs bomb forward down the touchline and Eriksen and Lamela make runs off the shoulder of the last defender, with our nominal centre forward also either making a run or dropping deep. This will allow Holtby to pick up the ball, turn and then play the long pass of his choosing to either a) the wide full backs, b) the wing players who are cutting into the center as play progresses, c) the centre forward's run down the middle, or d) the centre forward himself, who's at this point dropped into a deep position to offer Holtby a quick forward release.
3) Possession phase:
______________New CB___(halfway line)___Verts_________
Bentaleb-->------->--------><---------<-------<------Schneiderlin
----------------------------Holtby position 1------------------
OR
--------------Holtby position 2--------------------------------
I
\/
Walker----Lamela----------------------Eriksen--------------Davies
___I___________________(penalty box)_ __________________ I
--I----------------------New CF------------------------------I
\/----------------------------------------------------------\/
___________________(goalline)____________________________
In this third phase, Holtby will again prove crucial: either by directing play from deep, with Eriksen and Lamela forming passing triangles with either the CF or with a wing-back (both of whom bomb down the outside providing width), or with Holtby rushing forward to be the playmaker in the middle, allowing one of Lamela or Eriksen to make a run into the defense while the other buzzes around providing Holtby and the strong, supporting CF with a pass-and-go option. Either way, our needs seem settled: we'll have a strong defense, given that's being screened by two immensely athletic, technically excellent players, and a quick offense, if it's pulled off. It is also a system that, as much as possible, plays to Holtby's strengths, and thus one I think we'll see at some point.