Okay so Inspire Courage says
At 5th level, and every six bard levels thereafter, this bonus increases by +1, to a maximum of +4 at 17th level. Inspire courage is a mind-affecting ability. inspire courage can use audible or visual components. The bard must choose which component to use when starting his performance.
Then we have some races with alt Skill bonus that read like this
Bard Choose one bardic performance; treat the bard as +1/2 level higher when determining the effects of that performance.
Now I know it says maxium but it seems more like because of the level cap of the phrasing... or perhaps I'm just trying to get around it in my own head. Since I know you can get past the +4 with Dervish of Dawn and Dervish Dancer. So for example lets say I took 12 levels of that and applied it to my bard. So that when he hits level 17 would it became a +5.
Of course it should continue scaling past level 20. It has a clear progression and a game could hypothetically go past level 20, at which point due to lack of conflicting PF rules, 3E's epic rules would kick in and say that IC and other bonus progressions continue as normal.
Very strict RAW it does say maximum, so you are probably up the poo creek without a paddle. Fortunately, PFS stops at 12th level anyway (the point where this would start being an issue) and PFS is the major instance where "insanely strict RAW readings" would be an issue. Most home DMs would probably allow it.