The reputation system - even if not perfect - is mostly an adequate measure of one's "social capital," even if not directly monetized. The problem with using SP as social capital is parsing that SP.

Currently, you can earn SP from posting, commenting, and curating - or you can buy Steem and power it up into SP. Posting rewards can be split 50/50 between SP and liquid Steem. Commenting is split 50/50. Unless you have chosen the 100% SP option since you began creating content on Steemit (which wasn't even possible for users in the first few months, I don't believe), you won't receive that "social capital" under this proposed system. Anyone who had received the 50/50 payout and then powered up the other half - or any portion of it - will essentially be penalized. Even though they earned the "social capital" as a reward for their content, it wouldn't be recognized as such. Comment rewards and powering that up would be the same.

It all gets a little messy and I really don't think it's necessary. As stated in a comment below - we need to have additional/better incentives for holding SP. We don't need to further complicate the system. It's already complex enough for the average user. Finding more ways to use the different tokens and to encourage people to want to buy, sell, and hold them should be the priority for development.

I like that we're discussing new and different ideas. I just don't think this is a particularly good one. It doesn't solve a problem and it doesn't increase the desire to hold or use the currency.