I'd say it will be more difficult. Toyota and Yamaha have already extracted another 60 bhp from the engine going from the IS F to the RC F so you need to work even harder to get more.
Some of the extra power was from redesigned intake and exhaust headers, but to get more, and to maintain reliability, they needed to go for expensive internal lightening and balancing, to get an extra 500 rpm - they wouldn't have bothered if it was easy to get additional power with a remap and an exhaust.