Tremor is pretty easy to do.
According to the latest patch notes where it was mentioned, it now correctly pulses every 3 seconds.

Divide 3 by the number of shaman's in your team.
This is the ideal interval in seconds, between Tremor drops.

With 2 shaman's, you'd like a Tremor dropped every 1.50 seconds.
With 3 shaman's, you'd like a Tremor dropped every 1.00 second.
With 4 shaman's, you'd like a Tremor dropped every 0.75 seconds.
With 5 shaman's, you'd like a Tremor dropped every 0.60 seconds.

Just make yourself a castsequence macro, within warcraft.
Or set your broadcasting software to round-robin the keybind Tremor is on.

The important thing is to not drop Tremor via the 4-totems at once new feature.
You want to stagger them.

I run 4 Shammies with a Prot Pally.
So my ideal pace is a Tremor every 0.75 seconds.

Even if you have an addon show how often it is until the next one pulses...
You will manually have to drop the totems initially.
And you will manually replace the totems as they are destroyed.

It's pretty easy to just spam the key a second time, if needed.
I cannot see the advantage of knowing that Shaman #3 had their Tremor destroyed.
For this to work, you'd need a separate keybind for each shaman on your team.
So you could replace shaman #3's Tremor, without the others dropping theirs.
It would be so much easier to just spam one key, a few pressed over 3 seconds.