First target was budget. This build came in under 200 mil inf. I used @Sovera's guide to fund it using merits earned from TFs while leveling. That's why it lacks purple sets outside of the ATOs.
Second, Hasten is about 2 second from perma, and I'm totally ok with that, maybe.
Third, was max HP so the scaling resists from SR kick in with a bigger HP pool. I got it to 2698, good bit shy of 2800 or so I was shooting for. I had plans to use different sets originally, but this build came in under budget. It plays pretty well, and I've been enjoying too much to go back and revamp it yet.
Fourth was incarnate soft cap defenses in four toggles.
I was using Soul patron pool for gloom and Darkest Night, but, like you mentioned, I wasn't married to gloom. Also, I wasn't really using Darkest Night that much. I almost went Energy mastery, but I decided to give Mu Mastery a try. I'm so glad I did. It really compliments DM. Two fast animation AoEs with good radius. I am toying with the idea of dropping Dark Consumption for maybe Static Discharge to see how it performs.
The next tanker I'm working up is a Shield/DM as well, but I haven't decided on a build for that myself. SR is so cheap on slots I was able to pump a lot of them into DM and Patron Pool.
Shield isn't that lucky, so if I do decide on a build I will post it here.