I've been thinking about how sorcerer and warlock subclass themes interact for a while, and there is definitely still some lingering holdout of 'ancestor was a magic creature' in the subclass. Draconic being the most notable with the whole 'ancestor was a dragon' (or the description actually calling out 'making a pact with a dragon' thing).
I do think it would be a good idea to move sorcerer away from the magic creature/bloodline theme altogether, in order to make the differences with warlock more obvious.
The truth is, the lore for a Sorcerer and the lore for a Warlock are virtually identical. It is possible for a character to make a pact with a Dragon to become a Draconic Sorcerer, and it is possible for a Warlock to inherit the pact from an ancestor who made it.
Sorcerer and Warlock can easily be the same class − and many say they should be.
That said. The main theme of the Sorcerer is the magic is "innate". So it is easier for the lore for the Sorcerer to "inherit" it. On the other hand, if the Warlock is magically altered by the pact − which makes the most sense since it is in lieu of studying − then the Warlock would also be casting spells "innately" from that point onward.
Ultimately, I want the Wizard character to also be able to cast spells innately. The Wand is an option, but innate should be an option as well. Cantrips especially can convey the flavor of innate magic.
In 3e the Sorcerer was mainly the only class that was a "non-vancian" spellcaster. But in 4e and 5e, there are no "vancian" casters, so the Sorcerer has lacked a reason to exist as a class.
For fans who love the Sorcerer class, the main appealing connotations are innate spellcasting − somewhat like X-Men superpowers − and aggressive combat magic. Since all classes need to contribute comparably to combat and since "innate" belongs to too many character concepts, 5e lacks a way to express these concepts as distinctively Sorcerer.
As it turns out, the 5e Sorcerer is evolving in a way that a noticeable characteristic is planar magic. It seems to me, the Sorcerer should be all about planar magic, affinity with a specific plane, the ability to planeshift back-and-forth with that plane, and relationships with the various creatures of that plane, is a distinctive way to flavor the identity of the Sorcerer class.
Then the Warlock pacts are more about a relationship with an individual creature.
Even here, the Warlock and Sorcerer can easily be the same class mechanically. But each has its own fan base who would feel a loss if they merged.