Did half an hour on Dr. Boom on the 2.3 PTR about two hours ago, mostly to test Quagmirran's Eye proc rate and internal CD.
I can confirm it to (still) have 45s internal CD, 6 seconds duration. 10% proc rate appears likely - my longest chain was approximately 17 casts after proposed internal CD was over. In no other case did more than 11 casts pass.
Here is a WWS parse.
Since a lot of silly things are going on in the WWS I made a quick guide to the 16 observed Quag procs and their timings:

07:16:24.915 [Scorch spam starts.]
07:16:26.862 You gain Spell Haste.
07:16:33.095 Spell Haste fades from you.
Time since spam start: 1.947s
Duration: 6.233s
07:18:04.402 [Last spell before OOM - spam stops.]
07:18:21.551 [Scorch spam starts.]
07:18:34.515 You gain Spell Haste.
07:18:40.514 Spell Haste fades from you.
Time since spam start: 12.964s
Duration: 5.999s
07:19:21.189 [Last spell before OOM - spam stops.]
07:21:42.996 [Scorch spam starts.]
07:21:42.996 You gain Spell Haste.
07:21:48.952 Spell Haste fades from you.
Time since spam start: 0.000s
Duration: 5.956s
07:23:12.779 You gain Spell Haste.
07:23:19.045 Spell Haste fades from you.
Time since last proc: 1m 36.049s
Duration: 6.266s
07:23:59.512 You gain Spell Haste.
07:24:05.407 Spell Haste fades from you.
Time since last proc: 46.733s
Duration: 5.895s
07:24:10.517 [Last spell before OOM - spam stops.]
07:29:01.762 [Scorch spam starts.]
07:29:03.965 You gain Spell Haste.
07:29:09.899 Spell Haste fades from you.
Time since spam start: 2.203s
Duration: 5.934s
07:30:08.641 You gain Spell Haste.
07:30:14.589 Spell Haste fades from you.
Time since last proc: 1m 4.676s
Duration: 5.948s
07:31:12.733 [Last spell before OOM - spam stops.]
07:31:26.151 [Scorch spam starts.]
07:31:28.291 You gain Spell Haste.
07:31:34.330 Spell Haste fades from you.
Time since spam start: 2.140s
Duration: 6.039s
07:32:25.790 You gain Spell Haste.
07:32:31.757 Spell Haste fades from you.
Time since last proc: 57.499s
Duration: 5.967s
07:33:12.273 You gain Spell Haste.
07:33:18.404 Spell Haste fades from you.
Time since last proc: 46.483s
Duration: 6.131s
07:33:22.704 [Last spell before OOM - spam stops.]
07:36:00.838 [Scorch spam starts.]
07:36:45.436 You gain Spell Haste.
07:36:51.466 Spell Haste fades from you.
Time since spam start: 44.598s
Duration: 6.030s
07:37:36.601 You gain Spell Haste.
07:37:42.826 Spell Haste fades from you.
Time since last proc: 51.165s
Duration: 6.225s
07:38:25.946 [Last spell before OOM - spam stops.]
07:39:27.453 [Scorch spam starts]
07:39:27.826 You gain Spell Haste.
07:39:33.819 Spell Haste fades from you.
Time since spam start: 0.373s
Duration: 5.993s
07:40:20.548 You gain Spell Haste.
07:40:26.409 Spell Haste fades from you.
Time since last proc: 52.722s
Duration: 5.861s
07:41:07.552 You gain Spell Haste.
07:41:13.311 Spell Haste fades from you.
Time since last proc: 47.004s
Duration: 5.759s
07:41:52.576 You gain Spell Haste.
07:41:58.824 Spell Haste fades from you.
Time since last proc: 45.024s
Duration: 6.248s
As can be seen from the WWS, I was also wearing Shiffar's Nexus-Horn and 2/2 Spellstrike during the test. I observed ~2.6% proc rate on the Spellstrike set bonus - assuming no internal CD like stated in OP here.
This post by Manly claims it has a 10s internal CD. Anecdotally, I do not think I've seen the Lesser Spell Blasting buff stacked on my character. If anyone can attempt to confirm the "non-stackability" of it, please do.
If anyone wants to analyze Shiffar procs from the WWS, you have my blessing!
