Currently, the platform has around 100K signup users (forgive me if I'm wrong) and only 30% of it are active.

What we have are 100k accounts but not users. I couldn't even be sure if we have 30k users. Many users have more than one account. Miners for example can make as many accounts as they like (at a small price) without the need for a reddit or Facebook account. I'm not a miner, so I'm not sure what the purpose of this is, but I think for whales it can be useful for curating purposes. (Again I'm not sure how but lots of whales have smaller dolphin accounts for curating) Possibly bot-run. Possibly it's a means of being more careful with the vote of their main account since voting like a bot with such high rewards could lead to problems (I'm totally speculating here).

if this trend will continue, what will be left behind in the platform are those friend of the whales and those who belong in their network.

This would be bad indeed. This would not be in the best interest of the whales and they know that if steemit became a sort of private club then steem will eventually lose value. Unless of course there is a new demand for steem. For example for another non-blogging platform.

lots of real writers came and signup for the community as a social media platform that will give rewards to those active members by posting and curating good quality contents.

Personally I think selling "steemit" to people as a way to make money is actually BAD for steemit. Steemit should be described to people as a "support network" rather than a social network where people get paid. Though I understand some day it will be a social network, in its current beta form I wouldn't describe it as one. I am indeed making friends on steemit, but they become my followers and therefore my supporters, and they offer not just upvotes but also critique and additional facts & ideas.

What makes steemit great is not that you can make money, but rather, that people are incentivised to write quality content and constructive criticism and to be respectful of each other, due to the small possibility of making a buck here or there.

If we set people up to expect big rewards, then of course people will return to Facebook where they don't have to feel that disappointment in themselves.

What if every time an article is posted, an instant reward will be given to that post right after posting it based on the author's reputation. For instance, if the author has a reputation of 60, then his post will receive an instant rewards of 60 SBD and if somebody will vote for the article, it will be treated as an additional rewards.

There are some problems with this idea because it is possible for users to sell an account with a high rep. However you may be on to something. Take a look at the most recent post by @dantheman where he talks about the idea of monetising reputation. :)