Can't your patron be a dark mysterious figure for a bit then remove their hood and "Surprise! I'm the Devil! Mwahahaha!"If you dont pick who to make a pact with, till 3rd, a warlock shouldnt even have a power though, you have no deal, no bargain, nothing.
I think the first level ability will be changed to something like "Eldritch Pact". All Eldritch pack will do is give you Eldritch Blast cantrips.
At first level, you can name your patron or keep them as a hidden benefactor. Their specific style of pact doesn't come into play until level 3.
Same thing with the sorcerer. You might have been born with sorcery and one time you shot fire at the neighbor's cow. However when you train to become an actual true sorcerer you had to push down and bottle up most of your origin in order to control it. Not until you got to level 3, when you fully control of it, could you start digging back into your origin your draconic ancestor, an aberrant infection, inner wild magic, or a shadow taint.
In most stories, the warlock or sorcerer have to learn control first before they tap into true power. Those who quickly get into in a magic or granted powers tend to either explode or get mutated.