Why? Sorcerers in 5e don't have spiritual allies/patrons. Warlock's do. You can map Djinn/genies to any of Warlock patrons rather easily, as Djinn traditionally have elements of all three, ie ancient spiritual beings, malicious spirits (shaytan djinn), and being creatures from another universe.
You seem to want to argue --nitpick, even, in the case of genies being patrons-- with people's character concepts instead of helping them realize them. Why is that?
I explained my reasoning here -
http://www.enworld.org/forum/showthread.php?p=6462689#post6462689 . In short, I don't think that warlock's necrotic magic is thematically appropriate for a djinn. That is all. If you want an elemental themed familiar with the sorcerer, that's fine, I have nothing against giving access to find familiar ritual. Sorcerer background also allows for extraplanar critters giving them magic.
And I'm just arguing against the multiclass rules being good. As far as I'm concerned, they're crap and should be tossed out, and replaced with something that actually works well. Most of the interesting story ideas in this thread are, as far as I can tell, would kind of be terrible with the rules as written.
The classes are designed with the idea tiers in mind. 1-4, 5-10, 11-16, 17+. At each new tier, there is a notable bump in power and capabilities. A barbarian-rogue would be trailing behind everyone else. Dipping is the only way the current system really works outside of very select cases (usually, half-casters switching to full caster for more spell slots).
And, because of that, non-dip multiclassing leaves you with ineffective characters that fall behind everyone else in terms of not only combat ability, but exploration and social ability as well. This very quickly becomes not-fun (TM).
It is only effective 1-2 level dips, then focusing on a main class. This isn't organic growth, this isn't opening options. I consider it to be an abject failure in that regard that requires GM house rules and intervention.
So, I see a lot of people saying they want to mix rogue and barbarian, or warlock and the like. And you know what? If I thought the current rules supported those kinds of characters, I would be all for it.
I think the rules are flat out worth less than the paper they're printed on. They are complete and utter crap at pulling of story driven multiclassing, and only support min-maxing.
There's a lot of "If you don't like multiclassing, then you hate Creativity! And you killed my character!" in this thread Which is just untrue. I will work with people to help them make their concept work, assuming I'm the GM, in a way that fits in the world.
That said, I've personally yet to find someone who's used this style multiclassing for anything beyond twinking their character. Allowing it isn't going to make characters deeper, or more special beyond notes on a piece of paper. You can still role play it out. If it comes up as an organic part of your character story, we'll talk it out and come up with a solution. But someone who plans out multi-classing? I find that's just encouraging meta-game focus on the sheet.
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