My personal opinion is that this idea could be very useful.
In my humble opinion... it should have more added to it... idea:
Name: Weapon Immunity Control
In-game menu to allow server-wide weapon immunity or only admin immunity. Menu would look as such:
1. Admin Only (ON or OFF shown to the right)
2. Deagle (5%, 10%, etc. up to 100% shown to the right)
3. FN57 (5%, 10%, etc. up to 100% shown to the right)
4. Elites (5%, 10%, etc. up to 100% shown to the right)
5. USP (5%, 10%, etc. up to 100% shown to the right)
6. Glock (5%, 10%, etc. up to 100% shown to the right)
7. AK47 (5%, 10%, etc. up to 100% shown to the right)
and on page 2 and so on list the other weapons.
If 7. AK47 was turned to 10% then everybody in the server would only take 90% of the damage done by an ak47. If 1. Admin Only was ON and 7. AK47 was 10%, then only Admin would be protected from 10% of the ak47's damage.
In addition, you could add commands for individual weapon immunity
amx_immune <playername or user id> <weapon> <immune%>- immunes a player from <immune%> damage done by <weapon>
amx_unimmune <playername or user id> <weapon> - removies immunity a player has from <immune%> damage done by <weapon>
amx_immuneinfo <playername or user id> - lists in console all weapons a player has immunity from receiving <immune%> damage for each individual weapon
amx_immunemenu or say /immenu - Brings up in-game server-wide immune menu
You could use nVault to store the data and make the bans permanent via steam ID.
These ideas may sound like too much or overkill on a simple idea, but you can look at a plugin I wrote called Restrict Commands [rc]
which has all of those features--except in relation to client commands. I use nVault and a menu and all of the above suggested features. You could mimick that code and just redo the arrays and functions to be related to damage done by weapons. It could be easily done using that plugin as an outline if you didn't feel like coding it from scratch.
In addition, the % for the menu is simple to add as well.
I think that would make this a beasty, awesome plugin in many respects. I would, myself, use such a plugin if you used all of those ideas and features in context with the idea of weapon damage immunity.
If Joe gets killed by awps all the time, I could go in console and type
amx_immune joe awp 40
Now Joe will only take on 60% of the damage done by Awp's--giving him a fighting chance.
If everyone is awping and dying by awps, I could go into the menu and turn awp immunity to 95% and only 5% of awp damage would be taken by all players server-wide--or if Admin Only is turned on--only Admin would be protected.
These are just ideas... that's all.