don`t say its impossible, I believe its possible, but it would need to... how to say it?
recreate GBA mode from a scartch and then make a GUI for it so people will be able to use it without memorizing commands like /save or so, since its too hard for them
but my real reason to post this message is...
DSi got 133 MHz processor speed, indeed, but it is still the same type of CPU, it just upgraded version of the original, its not some MIPS OMAP3 new OMFGZ THIS IS THE ARCHOS 5! cpu, its nearly twice better then the original DSL cpu (which isn`t much really), while the second ARM 7 CPU is the same version with a similar limitations that is meant for the WiFi connectivity, Touch screen and I believe the Guitar Hero Grip on the DSL\phat uses it too (though I am not sure)
now you might think that power is all what we need to emulate the gba, but the one to actually make an GBA emulator needs to either know both of the GBA or its documents pretty well and the DS or its documents pretty well, the one who created an emulator to the DSi used a similar CPU power to the PSP (400 MHz MIPS) and simply ran the GBA emulator that was created within year or two to the PSP, who is much more powerfull then the DS, and compared to our "hack", the PSP's hack allows to use different operation system rather then opening an operation system on an operation system (opening the DS OS first which opens the DS cartiage which got the OS files) which gives much more options, since all its modes are "hacked" and "allowed to be accessed" unlike DSi mode, which is still not hacked, I bet that the DSi mode is hackable (everything is hackable, but you know what I mean, its not a PS3) but theres no reason to hack it, why? the new processor will only improve the emulation speed done so far, it won`t open a new one, now to compare the numbers you given to the ones you`d understand more...
I hold a cellphone model Nokia 6120C, it costs nearly as much as the DSL does (at least in Israel), and its CPU is ARM13 CORTEX 166 MHz and 32 MB ram, it can emulate the GBA at 11-14 FPS and I overclocked it [cell phones minifans really do their job!] to 240 MHz, and it gets to 20 FPS, I have no idea how the GBA emulator for the symbian language works, however it emulates nearly as well as the PSP models and it has lower "power", how does it do that?
CPU's and GPU's and RAM can`t be measured with their amount or speed, if it was meant for emulating, it will emulate, if it was meant to games, it will play games, if it was meant for documents and office work, it will do that, the reason why CPU's and GPU's and RAM's can do all three of those stuff is because we are in an advanced world, with a high-end technology, the fact it does all that is good but it still means it does what its meant to do better then everything, sadly Nokia is having many gadgets in their junkphones, and they can`t code different engines for all their junkies, they pay other people to create an engine (Bluetooth company coming with Blueshell, and the camera "Cybershoot minizure" having its own engine which I don`t know about, Opera browser, File browser, Real player, all those options are simply "part" of the operation system) however thos parts aren`t really created by Nokia, Nokia is using emulating as their key to use them all at once in one cellphone, therefore my cellphone CPU was meant for emulating, and it does it well, the DS CPU however was meant for games, the structure, build and memory are built differently, acting differently and provide different outcomes, hence why certein GPU's with 64 MHz's are running games better then some 512 MHz's GPU's (like Nvidia Geforce 74 and Nvidia Geforce 88, one was meant for games and one was meant for work, but both of them can do both, only one does one thing really well and the other does the other thing really well)
if you want the purest example of it, try to run Lego Racers on GPU's\graphic cards that are meant for graphical work and edit, see how messy it will become on certein levels where the CPU barely understands whats to do as its sole purpose is open extreme high graphic editing softwares that you are not able to start