I don't have a firm answer yet, because RC costs depend on real costs, and code optimizations are changing the real costs. A good example is the new json parser lowered CPU cost of custom_json ops. But probably the biggest change will be that we're now accounting for signature costs, which was previously ignored by RC calculator.
So RC costs will be one of the last things we know, as it will be last change to hived before hardfork.
But I do suspect that costs of custom_json will go up (because of aforementioned signature time being included in costs now) and the RC code does increase costs during network congestion. Making that work optimally though will likely require tuning.