Like all the loaders, metldr is a SPU self designed to run in the isolated SPU.
lv1 (ie the hypervisor running on PPU) is responsible for loading the metldr self into the isolated SPU with the necessary arguments & dealing with the outcome.
The metldr self binary is stored in lv1 memory at a static offset, ready for lv1 to copy when necessary.
Statistically speaking, you cannot bruteforce the ecdsa encryption on a PC (or even a distributed network) in a reasonable amount of time, at least not unless you find a weakness in the encryption procedure used to produce your encrypted target.
Keeping in mind anyway that bruteforcing is illegal, punishable under US federal law.
However it is perfectly legal to run a custom SPU executable that may read data from the isolated SPU memory & transfer it to the PPU.
The isolated SPU, like its name suggests, uses reinforced security, the local store (0x40000 bytes of memory reserved for each SPU for storage) is purposefully inaccessible to reading & writing by the PPU code, DMA/MFC access is disabled & the only way to exchange data between the isolated SPU & the PPU is mailboxes.
If lv1 (and maybe only lv2) is jailbroken, it is possible to write a PPU app that loads a isolated SPU payload which in turns loads metldr with appropriate arguments then using interrupts leaks data back to the PPU. The mailbox being limited to 4 bytes transfers, the interrupts are used as a synchronisation mechanism, signaling each mailbox 4 bytes reads/writes, until the entire data is collected & made available to the user. That's exactly what the ERK dumper (by flatz) does.
Using this technique, it is possible to leak crucial encryption keys (in unencrypted form) like the eid_root_key, a decrypted elf or whatever data you may be interested in. Currently this technique is only used on consoles where the hypervisor is jailbroken but it might be possible to adapt the technique to a situation where only the supervisor (lv2) is jailbroken, it needs confirmed though.
From here, there are 2 possible steps forward.
1. Wait until lv1 on metldr2 consoles gets jailbroken so that existing code can be used to leak data.
2. Try to adapt the existing isolated SPU leak code so it runs at supervisor level (lv2) rather than at hypervisor level (lv1).
There is already one publicly available supervisor (lv2) exploit on metldr2 consoles (used by ps3xploit PS3HEN) which was directly ported from the sceNetIoctl Vita kernel exploit used for a time in henkaku.
And I have another supervisor exploit that I keep private for the moment.
Given the relatively slow but constant progress made with metldr2 consoles over the past 3 years, and I am not talking just about the ps3xploit work btw, others have worked on one thing or another, I am confident that the hypervisor (lv1) should be exploited within a year or so by someone, who knows, after a while we may even end up with different exploitation options from different people. I expect that metldr2 will eventually lose its secrets.