Looking at the mechs:
The commando should not get ECM at all. No production variants ever had it. In addition, they gave it to the most prolific variant out there, the one that has more missile hardpoints than any other light mech.
The cicada is the same. No production variants ever had it, but they give it to the most expensive variant.
The D-DC should not get it either as it is the wrong variant. The K2 had ECM much further in the future but not the D-DC.
The jenner is in the same boat as the atlas, a variant has ECM in the future (10X), so it has as much of a right to it as the atlas, especially compared to the commando and cicada.
The cataphract, hunchback, and awesome are in the same boat as the jenner, but they also do not get ECM.
The dragon, catapult, and centurion are like the cicada and commando, no production variants ever had ECM, but unlike the commando and cicada they can not use ECM.
The only mech that should have it is the raven 3L.. But the 2X and the 4X are still inferior in most every way to the jenner and will remain that way as they also do not get ECM as an option.
Looking at the equipment:
BAP – Everyone can use BAP, even mechs that never had it on any variant, like the commando, jenner, awesome, catapult, dragon, cataphract, centurion, and hunchback.
TAG – Everyone with an energy hardpoint can use TAG, even mechs that never had it on any variant, like the commando, cicada, jenner, atlas, awesome, catapult, dragon, cataphract, and centurion.
NARC – Everyone with a missile hardpoint can use NARC, even mechs that never had it on any variant like the commando, atlas, awesome, catapult, dragon, cataphract, centurion, and hunchback.
AMS – Everyone can use AMS (even though when it was introduced for all mechs some people complained on the forums that it would be the death of LRMs, but I digress), even mechs that never had it on any variant like the commando, cicada, jenner, awesome, catapult, dragon, cataphract, centurion, and hunchback.
Personally, I think all mechs should get ECM as an option. In addition I think they need to BUFF ravens, not nerf jenners to give them more parity. Let all ravens use 300 XL engines. Give the 2X and 4X 3 module slots (like the jenner K) instead of 2 (like the jenner D).. and give the 3L 4 module slots to make it superior to any jenner. Do not balance the raven with the jenner through a single piece of optional equipment on a single variant because 2 out of 3 variants will still be crap.
Buffs not nerfs.