I understand that worry, but it doesn't make much economic sense.

It is possible that some farmers would abuse it, but that would be expensive and unnecessary, since the target weed would die with a regular dosage.

Abuse of glyphosate spraying is also counter-productive. Low volume sprayings are generally more effective.

And by the way, glyphosate-resistant does not mean glyphosate-impervious. Non-targets can still be harmed.

The risk of over-usage of glyphosate is re-enforcing naturally occurring resistance in target weeds. Glyphosate should always be used at intervals, with different herbicides filling in the gaps.