Of course, this means that there won't be a single ECM-capable heavy for quite some time for the Inner Sphere- most 3050-era ECM users are lights or won't show up for 5+ years or both.
All except one. That would be...
The Cataphract. It had ECM capacity before the GECM system even came back online.
Wait, what you say? Let me explain.
3025-era tech had what was called "Electronic Warfare" equipment, a heavier but inferior combo of what the Guardian and Beagle Probe did. That is, it's ECM bubble was 90m rather than 180m, and it's "Beagle" only gave half the reach the Beagle/Clan Active Probe do. Being 3025-tech, it was also bulkier (7.5T and 4 crits)- but it was built into two machines- the original Raven and Cataphract.

The "-0X" packed a PPC, AC/5, and two medium lasers along with the EW gear and a remote sensor dispenser. (The same EW gear was on the original Raven, the -1X.)
It could be added as a standard choice or as a Hero- and the EW package could also be given as a broader option choice than the higher tech ECM for use in more chassis.