Brewology

Has there or can there be a Homebrew ISO loader?

There has been in the past, yes... Why? Isn't there one already built into the custom firmware that you're using?
If you're talking about the Go, then there probably won't be...
ISO loaders have to be constantly updated to work with the newer firmwares, so it would be more difficult to port a modern one to to Go.

have you seen the new HB loader? I showed you... runs N64 better than all the other FIRMWARES can. I think an ISO loader is in order... if not, a freakin firmware already!!!

You've got the wrong idea about homebrew....
Whenever you find an exploit, there are different things you can load through it...
Sometimes, you can't load anything at all. Sometimes, you can only load like 200Kb and nothing else. Sometimes, you can link that data to other data and while you're only able to load 200Kb, you can use that data to load more data. Sometimes, you can load any amount of data and you can have access to read any flash files. Sometimes, you can read and write any data anywhere.
Now, look at what kinds of exploits we've had in the past. Most of the time, they could at least read the flash files. Those are the files needed to run .ISO files. Sometimes, you can flash over data to the other drives on the PSP like in the 1.5 firmware. However, this exploit doesn't allow either and that's why you cannot flash anything or run certain games like the .ISO loader.
It's very difficult to make the PSP grant you access to other privileges and it can be close to impossible at some times. You need to either wait for someone to unlock that power or find another exploit. There are some more floating around and I'm sure at least one of them allows access to the flash0:/ or flash1:/ drives.