I've been thinking about this.
Most of the sessions I've done on A800s have either been long ago, on 456 or 468 (where the 500nWb/m issue would be moot) or at 15ips, where erasure is better on every machine. I'm sorry if I jumped to a mistaken conclusion about these machines. I know I had no problem with my A80MKIV, and we have no such problem with our A820s.
I have run into problems on older machines with high-output tape, but the problem is generally in the record EQ, where there isn't sufficient "cut" available for flat 30ips recording. I recently had a problem in a big fancy studio with erasure on an A827, but it was an adjustment problem, not an un-avoidable one.
I find it hard to believe that sufficient drive current isn't available (possibly with a modification to the erase master amplifier with different output devices, if necessary) to erase 30ips 500nWb/m. Seriously, if I couldn't run-over take one with take two, I would stop the session and go elsewhere, and if I owned a machine with that problem, I would do whatever it took to fix it. Spending half my time erasing is simply too much to ask.
I would love to hear a solution to this problem, if it is a general one and not specific to one machine, for A800s. Any modification suggestions welcomed.