Another option, other than SoS, is a rank-based system. C-Diplo is one option, though the Carnage system is gaining a lot of popularity in Face-to-Face.
A modified form of Carnage could potentially work here, and it would work for variants as well.
In a solo, the winner still gets all the points.
All draws are DIAS, but you don't share in the draw equally. Instead of your points being based solely on SC counts, they're based on your rank in comparison to other players.
Rank is determined by final SC count, or for eliminated players, how long you survived (the longer the better).
In a standard 7-player match:
7000 for 1st
6000 for 2nd
5000 for 3rd
4000 for 4th
3000 for 5th
2000 for 6th
1000 for 7th
Players that tie for rank split the points for all applicable ranks. Two players tie for first, for example would get 6500 points each. The next-highest player would then be ranked third.
This point value would then be trivially converted into vDip points as (YourPoints / AllPointsAwarded). In a seven-player match, this means the board-topper would received about as many points as what they'd get in a four-player draw.
(A slight modification to this system can give 0 points to the last-ranked player and 1000 fewer to everyone else, though generally some points are allocated to last place for a non-solo scenario as a small incentive not to throw the match, assuming that player hasn't yet been eliminated. Making such a modification increases the % of final points held by those in top ranks.)
This system can easily expand to adjust to the number of players. While true Carnage also grants one point each per SC held at game's end (with all 34 granted to the winner of a solo), this is really only used as a tournament tiebreaker, and it would have less value here.
The pluses of this system:
- It encourages players to weigh the relative merits of holding a firm stalemate line versus jockeying for position. As such, it can add some unpredictability to the late game.
- It discourages draw-whittling, as it's unlikely to make an enormous impact on the final score whether a single power with 1-2 SC's remains on the map.
- There's a more significant difference between the points an individual can receive in a solo versus the best one can receive in a draw.
The minuses of the system:
- Because draws aren't shared equally, to some this feels like a betrayal of the original rules.
- While I personally see the impact on the endgame as a positive, it can change the character of the typical stalemate-line staring-match, which some may object to.
- After being eliminated, your eventual final score is dependent on factors that you no longer have any influence on. If the game ends in a draw, you may get points; if it ends in a solo, you get nothing. Modifications to this system can adjust for this situation, though they could bring back the emphasis on draw-whittling in a zero-sum environment such as this.