The majority of the restricted blocks and placement actions are possible anyway with workarounds

[GavJenks]

TNT / explosions:

• You cannot place it directly, and you cannot put it into a dispenser by standard clicking.
• You CAN however, place a hopper over a dispenser, drop TNT into it, and toggle the dispenser to activate TNT
• You CAN also place TNT carts without any restrictions.
• You CAN place end crystals which also explode.
• You CAN place beds which explode in the end or nether
• You can probably (haven't been able to test, but based on the above being possible) spawn a wither which may then proceed to blow up all sorts of things
• You CAN place creeper eggs then stand near them causing explosions
• You can set off and harm people etc. with fireworks explosions
• Possibly others I haven't thought of
• Note that this also gets around, indirectly, various other restrictions, for example you can use TNT to break reinforced chests

Water:

• You cannot dump a bucket directly or click a bucket into a dispenser inventory
• You CAN place ice and wait for it to melt into a source block
• You CAN use a hopper to get a bucket into a dispenser then use it for water or lava, like above

Getting into bastions:

• You can't get in if teleport is on, as far as I can tell
• You CAN still get blocks and entities to go in, though. Like to launch shit like TNT into the bastion and still blow things up / kill people / etc. Or send in mobs, and so on.

Fire:

• You can't click with a flint and steel (don't remember if dispenser flint and steel works)
• You CAN once again use a hopper to get around the dispenser even if the dispenser does block (i did test that)
• You CAN click with a fire charge without any restrictions (this is one of the most portable and easiest ways to kill players or mobs)
• You CAN set fires with some various side effect methods like beds exploding which add fires. IIRC (haven't tested this one) TNT also generates fires for flammable blocks in radius (see above TNT workarounds)
• On servers with fire spread, you CAN use a hopper to place lava and wait for it to light wood etc. on fire.

[Lazersmoke]

This is a can't/won't fix IMO, needs @TealNerd's verdict.

[GavJenks]

? One can fix a ton of these. Hopper management in particular goes a long distance here. And a large number of other things are just adding items to block lists that are obviously just forgotten, like fire charges, TNT carts etc.

Unlike the pvp issue, that involves a large number of overly restricting changes to fix, most of these are obscure nonsense that 95% of players don't use in the first place unless trying to get around stuff, like end crystals, etc.