There are some proof of concept/laboratory grade things involving the decapping of chips (recall reading one for dumping CPU keys from 360s without other hacks), things involving high end side channel approaches on a per boot basis, and things like snaking a wire through a BGA ball nest to get at a certain one on the underside (no alternative points). Mechanically speaking some of the chip quasi decapping things (see kamikaze attack on later 360 DVD drives) I have seen are not that difficult (the spot to hit is huge as far as milling and such operations go) but lack of tooling for it among the hacker and probably even more so forum reader set is going to add things there. Most other mechanical things are not so bad, and usually amount to shorting a few points temporarily. Seen less in the way of trace cutting for hacks compared to repair/diagnosis, circuit modding and similar such things though.
Ignoring that the list of annoyances seems to run
Needs high end electric test equipment, programmable chips or the like. Seen a few that warrant then big boy FPGA chips.
Needs modest programmable chips but associated gear as well (your pic chip might be pennies but the programmer is not, can't we use an arduino?)
Needs basic things you can probably buy from a real world electronics hobby shop.
Soldering seems to trip people up a lot, though I think I also got lucky with my cheap soldering irons (buying them from an electronics shop aiming at return customers was a good plan it seems) and have a fair bit of skill in the matter as well.
Oh getting PCBs ordered even if we give you the gerber files, parts list and a place to go.
Soldering has probably caused more problems than disassembly has but still seen plenty of ripped ribbons and borked sockets.
If you have to install Linux on something that trips people up, even more so if it in turn messed with local networks (still giggling about ARP poisoning attacks for 3ds pokemon scanners and people hoping Windows way past the XP version it was patched out of had raw sockets)
I am not sure what is easier between custom USB/SD drive format and network delivery. If you are familiar with computers in general the network thing is probably easier but if setting a static IP or even getting your router to do it is not something you can possibly do from muscle memory then maybe not.
Related to that might be needing unique per device keys and retrieving them to feed back into the build tools.
Temporary things also seem to frustrate some if they have to be redone. Possibly up there is failure prone methods (still remember doing a friend's PSP with the then new chickHEN package that saw a supposedly 1 in 4 or so success rate but after the initial success and running psp ident to get keys in case they were needed I thought I would be a good boy and reboot despite it only being advised, 20 tries later I get it to work again).
Not following guides and trying to colour outside the lines (usually mixing and matching regions, or trying to skip several steps instead of getting it working first and then doing the fancy stuff) is what causes most drama and trauma though. That and cheap media.
Upgrading from earlier hacks causes some troubles as well if the newer stuff wants a stock machine to start with and hacked versions might not have backups of stock, or backups from a far older version than will do of stock.
Most things also take to homebrew or ROM hacks (assuming they can and are not signed code only) fairly easily, though I have seen a few out there.
https://marcan.st/2011/01/safe-hacking/ is a choice link at this point as well.