Wouldn't it be most logical and intuitive if the [Upload] button in the IDE would function as "Upload Using Programmer" when someone has "Arduino as ISP" selected? I tend to click the button to upload when I am using a programmer for for example an Arduino Prom Mini board. And then I accidentally re-program the programmer board (an Arduino Nano) instead of the slave device. Very unpractical.
I actually would suggest a change in the Arduino IDE to accomplish this.
The problem I see with this proposal is it provides a simple way for a beginner to use the user interface to put the Arduino IDE in a state where normal uploads no longer work. It's very common that when people are having problems uploading, they start trying different Tools > Programmer options (because they have no idea what that menu does, or even what a "programmer" is. So then they end up with two problems compounded.
The number of people who would be harmed by this change is larger than the number of people who would be helped by it.
That could perhaps be mitigated to some extent by the Arduino IDE adding some output when the upload fails under these conditions "Tools > Programmer > Arduino as ISP causes the upload button to act as Upload Using Programmer, for normal uploads, please select a different programmer option".
For me, I want my IDE to act in a consistent manner, rather than having special behavior based on an arbitrary menu selection. If this were to be done, I would prefer it was done universally for all programmers, rather than for Arduino as ISP alone. That would require the addition of a default "None" option to the menu (which is actually not a bad idea by itself).