>The resistance can then be immediately removed and boost would become available instantly because it would be spinning near the full-boost RPM
You don't need to remove the resistance to get boost if you've only used the resistance to avoid overspeed. You've limited the turbine to max RPM and thus max boost. You only need to remove resistance or even reverse it and have the electric motor spin up the turbine when the RPMs drop below the boost value you want.
Yes, good point. Though I see this technology being used like KERS was used to preload the suspension and improve cornering. Mini boost spikes would be a possibility. In fact, an extra bit of power at the right moment can preload the suspension, too. I'm not saying they will cheat with it, but they will find a way to bend the rules a little bit. After all, you are only racing if you are cheating. :)
You don't need to remove the resistance to get boost if you've only used the resistance to avoid overspeed. You've limited the turbine to max RPM and thus max boost. You only need to remove resistance or even reverse it and have the electric motor spin up the turbine when the RPMs drop below the boost value you want.