Expertise messes with the Bounded Accuracy a bit...
You're reading the mechanics backwards. Bound accuracy is bound by the DC's needed, not the bonuses to hit them.
Keeping the DC's in check is how the mechanics enable PC's to complete the same actions Higher bonuses do nothing more than succeed at the same checks more often under pressure.
What bounded accuracy was "fixing" was the cycle of increasing DC's to meet the increasing bonuses possible.
The way it is now, a 15 DC check does the exact same thing whether it's completed by a fighter with a +5 bonus or a rogue with a +7 bonus (because that's the difference at 1st level), or a fighter with a +11 bonus or rogue with a +17 bonus (the difference at 20th level).
Excess bonus is superfluous and bounded accuracy works as intended until DM's start messing with the system.
In the example above the rogue and fighter should both automatically succeed on that check when not under stress etc, and should both succeed on a 25 DC check (1st level) with the listed bonuses and a 30 DC check (high level) by spending 10x the standard time when there's no risk for failure. This is true because there's generally nothing stopping retrying until successful.
Succeeding more often under stress isn't an issue because the expectation is that players succeed at checks. Succeeding can't break anything unless the DM overpowers the results of successful checks, which is still an issue regardless of bonus.
The only impact expertise can have on bounded accuracy is with opposed checks against other PC's who can make a big bonus and it's not a PvP game.
That's why expanding outside of the core rules and creating feats or more options to pick up expertise wasn't a big deal stepping on bard and rogue toes. The overall effect has diminished returns from higher bonuses. Abilities that protect against low rolls like reliable talent do much more for success ratios than a bigger bonus.
Short version: impact is negligible and no fix required.
If anything, I think opening more expertise and expertise-like abilities in feats and class / subclass abilities was an improvement and has no impact on bounded accuracy.