The coin count itself does not really matter. Each 'coin', or unspent transaction out, has value represented in 64 bits. Whether it is 100 coins or 1 million coins, it will occupy the same 64 bits, the only difference is where the 0's and 1's are placed.
The amount of blocks and the algorithm are really the biggest determining factors.
Hmm,
So in your Opinion would an Algo switch to say X15 or groestl decrease the memory usage , or would a chain swap be required to see the full benefit of such a switch in Algo.