Engineering, Paramedics, Janitors, and the Heads having maintenance access is grand.
What isn't is cutting Security's access. A good chunk of the station is maintenance, ISD is expected to be able to find regulation breakers and search the station for them. I don't see how forcing ISD to rely on having to get others to drop what they're doing and aid them like this is a decent solution. As stated earlier this change could result in Sec having to grab the rare engineer or paramedic on some rounds to aid them instead of focusing on their duties, or having a head of staff lead them into a possibly dangerous zone. This also removes the opportunity for a antag to use a officer's ID to be able to navigate maintenance or a officer using his access to help crew evacuate or get around a breach. On a canonical/lore note, why would CentCom lock out it's own ISD from accessing maintenance zones? Their facilities and the Aurora itself has been attacked canonically by outside forces, while NT also has numerous competitors and a paramilitary group dedicated to destroying them. Doesn't make much sense to lock your own boys out of your station's vulnerable areas in that case.
For Cargo, see Seeli's post. The nice thing about the Cargo Techs having all maintenance access is being able to move crates around in the tunnels in case the main halls aren't passable and to search maintenance for bounty objects. Other than that, I've found the all-access as good a tool for antag actions as the warehouse.
Assistants losing their access would be nice. I don't really get why they have it still, being just greytide or bar RPers at most. I'd also argue that Liasons/Consulars should have full maintenance access as well, considering they're meant to be a vital role on the station as well.
There already are numerous alcoves for antagonists to set up shop, especially the more based oriented ones like cult. If you want to make maintenance more of a maze/antag hide out, I'd argue the best way is mapping more onto maintenance. More small side rooms, ladders, side tunnels.