The "fewer replacements" argument comes up from time to time.
I understand the basis of the idea, but is it really likely to make a difference?
Let's use Manu Tuilagi as an example as he's a pretty sizable centre.
At the moment with the usual 8 man bench, he knows that he may well need to play for 80 minutes. Although there are 3 backs replacements on the bench, 2 will typically be specialist 9's / 10's, with the 3rd being a utility player. If that utility player comes in for any of the back 3, then Manu is likely to play for 80 minutes.
So, even with the liklihood of often having to play the full game, he's still a monster.
The same goes for any of the really big players. It's rare that you'll have a replacement on the bench just for them unless it's the front row.
Would taking replacements out of the game stop someone like Manu Tuilagi playing? I really don't think it would, and he'd continue to have the same impact that he currently has.
Albeit that if someone does pick up a knock while tackling him (or being tackled by him), then their team is unlikely to have a replacement to come on.
In that example, you get a man advantage by having bigger players.
maybe there's an argument that props would be smaller if they didn't have replacements.
However, you'd go back to more uncontested scrums if they didn't have replacements, or abuse of the scrum law if a team has a particularly weak scrum (although I can't imagine any team would ever abuse that
)
The best case I can come up with is to drop 2 replacements.
The idea being that you then can't have a lock and a back row on the bench and therefore maybe your pack gets a little lighter in the 2nd half (I'm not sure it really would though)
.. and then instead of both a specialist 9 and 10, you have 1 player covering both, who is then less likely to be able to cover centre as well. (again, I can't really see that helping much as with a few exceptions, half backs are rarely known for their size)
There's definitely some merit to the idea, but I can also see a scenario where it makes the problems worse.