My guess is that it works the same as it always did, but you can't create Spell Points from Spell Slots that you have. You can make Sorcery Points, but not Spell Points.
First, the spell point variant in the DMG says:
With this variant system, a character who has the Spellcasting feature uses spell points instead of spell slots to fuel spells.
Since the rule only affects classes with the Spellcasting feature, Warlock's Pact Magic feature is not affected. This is reinforced when it later says:
The Spell Points by Level table applies to bards, clerics, druids, sorcerers, and wizards. For a paladin or ranger, halve the character’s level in that class and then consult the table. For a fighter (Eldritch Knight) or rogue (Arcane Trickster), divide the character’s level in that class by three.
Note the distinct lack of Warlock being mentioned. Warlock is completely unchanged under the DMG's spell points variant rule
Additionally, even though you're using spell points to cast spells, the mechanic used actually uses spell points to create a spell slot which you then use to cast a spell:
Instead of gaining a number of spell slots to cast your spells from the Spellcasting feature, you gain a pool of spell points instead. You expend a number of spell points to create a spell slot of a given level, and then use that slot to cast a spell.
So Spell Slots still exist and are still required to cast spells. Your character just uses Spell Points to create Spell Slots on-the-fly. It's also part of how they limit you from casting 6th through 9th level spells: you can only create one slot of those levels per day.
My reading, then, is that using Sorcery Points to Create Spell Slots actually functions identically. You don't (and can't) use Sorcery Points or Font of Magic to create Spell Points. You still use Sorcery Points just to create Spell Slots. You can turn those Spell Slots into Sorcery Points, but I don't see any way to turn Spell Slots back into Spell Points. You just don't get Spell Slots from your class anymore. Your class that has the Spellcaster feature gives you Spell Points. That's the only way to get Spell Points.
It's a very rough variant rule, however, so you and your table should expect to need to make a lot of rulings on use.