On the one hand, some might joke.

On the other hand, there's a stupidly expensive Qantas card that comes with 1.25 miles for every AUD spent domestically (in Australia) and 2.00 miles for every AUD spent internationally. The fee is $1200 (AUD). Translated to USD, that's about a $775 fee for the equivalent of just under 2 points/USD domestic and just over 3 points/USD overseas. There are also some base fare discounts and so on thrown in.

So, the way I see it there are a few options that DL has:
(1) Improve earnings. 1.5 SkyPesos/dollar across the board wouldn't be a crazy offering for such a card (they do it past $150k on the DL Business Reserve) - Alaska is rolling out a card that kicks out 3 RDMs/dollar on foreign transactions. Alternatively, bring back the Miles Boost at certain thresholds.
(2) Full SkyClub access.
(3) Somehow buffering MQD earnings when spending on Delta or offering an automatic discount. You already have the 15% reduction in award prices, so having a more expensive card that offered a flat 10% discount on paid fares wouldn't be nuts. Qantas throws this in as well.
(4) RUCs or GUCs at various spending thresholds. If you offer (say) a choice of one GUC or two RUCs at each $100k spent, that would go a long way.
(5) D1 Lounge passes. I think this would be dubious given how they've set up those lounges, but offering two passes (for up to two people) per year, or offering one at each of several spending levels, might be an option.

An automatic waiver into Silver (and Gold at a fixed spend level) wouldn't be amiss.

I don't think we'd see all of those things, but some mix of them would work. Don't forget that back in 2019, if you spent $60k on the Reserve you got two Miles Boosts that gave you 15k RDMs and 15k MQMs, so from a pure redemption perspective the Reserve card has gotten weaker (even if that was offset by improvements to status earning).