Who's this "we," Kimo Sabe?
If the diamond mod team tells the CM that they need another diamond mod to take care of the work load, they'll ask the CM to call an election.
If there are particular mod issues that concern you, or any of us for that matter, or if you feel that our diamond mods, or a diamond mod, are not performing up to standards then you can contact the CM, or, you can contact the mod team directly and address it with them to see if your perceptions are shared by the whole diamond mod team and / or the CM.
Sometimes, where we sit determines (and informs what we see) - we may only have a part of the story. In the case of how much work the diamond mods do in their roles on this SE, we (non diamond mods) for sure do not have the whole story.
I offer a reprise of SevenSidedDie's nice meta post here as regards what happens when the need arises as seen by the diamond mods.
Stack Exchange generally consults with and defers to the moderator team about how many moderators there should be. It’s more about what the team feels the need for than anything else. The process is pretty much that a CM drops by the mod chat and asks how many election spots it should have and then sets it up. It’s pragmatic and not really much of a discussion. Mods poke a CM about an election, a CM shows up and asks how many and sets expectations about SE’s ability to schedule it in, then goes off and does it. Resignation timing—for actual removal of the diamond and any announcement—is discussed if necessary.
Bottom Line: No
No, "we" don't need to think about a mod election until the diamond mods decide that their ability to handle the work load, as unpaid volunteers, could use another hand and they contact the CM to set one up.
And I'll make one further observation: I find the quality of moderation in the past two years (since the last election) to have been good. The diamond mods do a fine job as exception handlers and being all around good stack members. Beyond that, each of them has shown me that I can trust their judgment and good sense.