Is it a good idea to bring this into modern continuity? Well, first we should look at what really worked in the original proposal. First of all, it was deliberately set up that this wasn't the main timeline. It was an early version of an elseworlds story, an alternate timeline where they were free to introduce major shifts in the central narrative. That's not what is happening in the modern proposal.
Second, the actual proposal in the original story really felt way more fitting for the characters. Selina had retired as Catwoman, but was forced to don her costume again to help Bruce in a battle against the Scarecrow. They were both plagued by halucinations of being alone, and the only way for them to overcome their fear was to cast aside their secrets and embrace each other. It wasn't something either of them decided to do, but instead they realized that they NEEDED each other. I don't know how healthy that would be in real life, but boy was it amazing in the comic. The modern continuity doesn't really feature anything like that, we just see Bruce decide that this is what he wants and gets to one knee. It's not BAD, per se, it's just something you might see in any soap opera.
It's always dramatic to introduce a shake-up to your story like a proposal, but one thing that modern comics readers have really had beaten into them is that most of these major narrative shifts don't stick. The original proposal was set in an alternate timeline which protected it from the ravages of ongoing narrative, but this new plot development will very likely wind up devolving into some pale imitation of itself a few writers down the line.
SO... all that aside... yes, of course have him propose. Always, always, always favor mixing up the narrative over just letting it sit, ESPECIALLY if you're doing it in a way that's meant to allow the characters to grow.
Will we be incorperating this into our timeline? In all honesty, I don't think this is something Bruce, as I understand him, is capable of doing... or something that Selina would ever want. He is defined by his inability to change, and she is defined by her unquenchable desire for freedom. Any story like the golden age proposal that forced them to confront their need for each other would inevitably alter the bedrock of their character in a way that might lead to them not being superheros anymore, so no matter how much the two of them understand that they are meant to share their lives, this particular step doesn't feel like something my headcannon version of either character could do. They would forever be just out of each other's reach. Not the healthiest way for a relationship to operate, but if they were healthy they'd spend less time on rooftops.