There's no reason to expect that any proposal should ever replace an existing launched, healthy network site. EE.SE has a proven user base and track record to justify its continued existence, plus it covers some topical areas that wouldn't belong on a general Engineering site.
There's also no reason to require that we reduce the scope of this proposal to "get out of the way" of EE.SE. Overlap between sites is not a problem if they can coexist productively, as is the case with many launched sites including the trinity of SO, SU and SE. This is something we discussed a fair amount on the Data Science beta site, in the context of overlap with Stats.SE. Two sites can approach the same question very differently and bring different perspectives; this benefits the user who's looking for one or the other of those approaches or perspectives.
If the Engineering proposal has a successful beta period and does end up being launched as a network site, it'll only be after a lot more discussion about scope and overlap. EE.SE may end up slightly changing their scope in response to our existence, if they feel it's to their benefit and the benefit of the users. But the context of actual questions and answers in an Engineering private beta is critical for informing those discussions.
In other words, let's see how it goes; you can continue to influence this discussion and argue your position by committing to the proposal and participating in our private beta main and meta sites.