So I am currently playing a book-learned well educated lore bard at lvl 3, and I consider dipping 1, or in the longer run 2, levels of wizard. Looking through the different spells and options going forward, I realized that there was a lot of low-level spells that this characters really would like to learn. Most of them are utility stuff like comprehend language, mending, identify and so on. But learning all of them through the bard progression would take a lot of levels. And I already entertained the idea of getting ritual caster just cause it would make sense for the character to have a spell book and copy spells. Then I realized I could dip Wizard and get access to those spells, and a book. I am just curious how sub-optimal this would be.
The main reason I like this is that It would grant me enough known spells that I feel the character would like to know without having to sacrifice the powerful spells from the bard list. The MAD is of course a problem from an optimization perspective, but I am already rocking a int of 16 anyways. I would probably do the dip at lvl 5 after my first ASI. A problem with ritual caster is that it is a feat and I really need to boost those ASIs and think I would rather trail one level than give up on a ASI. How bad would it be to be trailing one level?
I play for the roleplaying first, narrative at close second and at the same time like the abilities and stats to reflect my character.
Sorry if its a bit messy to read, English is not my first language.
Edit: I know that I copy higher level wizard spells, according to the errata. Would be a lot cooler if I could.
As I'm completely underwhelmed by Superior Inspiration I don't think a single level multi-class into Wizard will hurt at all in the long run . Personally I'd take memorising 6 first level wizard spells (with INT 20), a few extra cantrips and a spell book any day over Superior Inspiration. Taking the multi-class a bit earlier than 20th level is a good idea: It means you've got time to train out any first level Bard spells you've learned and can now cast as a wizard. Depending on the campaign the long run may never happen so the decision then becomes what am I delaying by taking the multi-class?
For me the biggy is that you'll delay getting higher level spells by a level. In my experience that's particularly important for getting third level spells, so delaying 5th level in a spell casting class is a bit of a no-no in my book. For a lore Bard delaying 6th level means you delay getting your first bunch of magical secrets so I'd only pull the multi-classing rabbit out of the hat at 7th level at the earliest.
Having said all that, if you've got a narrative reason for doing it early then go for it. If you meet an arch mage willing to show you a few tricks at level 2 then that sounds cool. If you're a failed wizard perhaps start as a wizard and multiclass to Bard if that fits your character concept better.
 If I ever have a GM that enjoys putting my characters into an environment with a low probability of being able to grab a short rest then I may change my mind.
Dipping into Warlock and particulary hexblade has strong synergies with a bard, but is not the path for this character. A also don´t feel like dipping more than one or possibly two levels into a subclass. I doubt the campaign will go on till lvl 20. I guess we might reach a bit over 12, but that is probably gonna be years from now. Narratively the dip is easy to justify as we have a wizard in the party (played by another player) who was my characters tutor in history and arcana growing up. I guess the smartest thing is, Aescleal pointed out, to wait and do the dip at lvl 7. But then again, thats a long tie away and the characters might be to involved with hunting deamins and monsters that spells like comprehend languages is something that still matters to them.
If you're doing it for character development purposes then don't worry about waiting until some "optimal"/ideal level to do it. Do it as soon as makes sense for your character. Level 7 is when I'd try and aim to do it but if the opportunity in the story rocks up/has already rocked up dive in with gay abandon.