Didn't see that people had replied some more
Like said, you would likely replace your old uLaunchELF or even LaunchELF with wLaunchELF_isr that has HDD support and other modernities that are nice while also being full launchelf experience, so possibility for drop in working out for you is high there. Then it would be getting newest OPL ELF like 1.2 beta build and copying that somewhere on your HDD, such as __common/APPS and adding it to your new wLaunchELF main screen. OPL is still compatible with your "old" games with new compatibilities. It ain't broke, ain't nothing to fix, really.
That's pretty much what I have done, it's working for now, but I would like to update it someday to load games from an exFAT partition, just because it will make things much easier to copy games to/from the HDD, also because it's very very very slow doing any sort of change to games in APA now that I have a large number of games on there.
Like what people were underlining; With PS2 capitalization matters like it does on Linux and other Unix systems. you need to make sure you rename whatever app you choose as your booter to boot.elf instead of BOOT.ELF. This stuff does not matter on Windows but it absolutely does on other platforms. Even if you were to convert into a memory card based deal, it would not be really any easier to manage. Instead of having to use a FAT32 USB stick and manually copying stuff with wLaunchELF_isr to your HDD to update the homebrews, you would be using a FAT32 USB stick to manually copy new updated ELF files to your memory card. I personally do not see the difference. Speed, maybe, marginal but my HDD has far more disposable space than my memory cards. OK I have far too many memory cards and a 64mb one that has served me historically well but still I would not call it management wise "better".
I already do use USB flashdrives when I need to copy anything that's not a game to/from it. And yes, I have the caps right, I was just talking about file locations and names, not the caps.
At worst you would need to use the old launchelf to launch a new launchelf to manage the HDD better which is a funky matrushka doll situation but it works fine. As in, get usb FAT32 stick with wLaunchELF_isr, launch wLaunchELF_isr with whateverLaunchELF your HDD boots into, and use said wLaunchELF.ELF run from the USB stick to copy wLaunchELF from the USB stick to your HDD. Memory residence is a beautiful thing.
The new uLaunchELF_ISR is already just booting directly form the HDD using DEV2, the only issue is that it has to reboot to load the configuration file off the HDD.
Also, crucially, both wLaunchELF_ISR and OPL can save their settings on HDD. Dunno about "all the other apps" but these two will at least. for OPL you would need to use the shiny new wLaunchELF_isr to create a partition that is +OPL (not __+OPL not __.+OPL just +OPL) and give it some space as it would be also place to save game cover etc data and additional compatibility configs you can even update on the console itself.
That's kind of the problem I am having. I am only really interested in having uLaunchELF and OPL on here right now, and would love it if they could just completely boot right from the HDD with no other devices needed. But for some reason despite the fact that I have uLaunchELF's configuration file on the HDD, it still seems to only check the memory card, where I have to put a small configuration file that basically says "Load the configuration from the HDD instead and restart with those settings".
I would absolutely love it if I didn't need the memorycard at all. At least OPL seems to save and load it's configuration from the HDD just fine.
Ideally I want to revamp this setup when I can to just use an exFAT partition for my games, but I still want to auto-boot into uLaunchELF from my HDD when I turn on my system without needing a memory card or usb drive or anything else connected. Not sure how to go about doing that, if I can even do that, and without removing my modchip.