This question has been vigorously debated since most to the Glass-Steagall Act was repealed in 1999, showing the most consequential banking de regulation in the US came from a Democrat administration, just as did the act itself come as the FDR administration tried to eradicate the causes of the Great Depression.
The biggest problem with mark to market rules is that they introduce very high volatility in traded assets while making non-traded assets seem more stable. That has consistently proven to be an insurmountable challenge. Faced with repeated banking crises and most acutely the failure of Bankhaus Herstatt the Basel Committee was established to solve the problem:
Information about the history of the Basel Committee
www.bis.org
After deliberations (one US Treasury designee was from the Open Market Committee of the NY Fed and lived in Basel more a year working on this) they produced the Basel Accords, now is Basel 3, that all major banks globally must file. That is the best solution thus far, but still does not really solve the biggest risks.
Deutsche Bank has almost failed a couple of times since then, Swiss Bank Corporation failed and was merged, Credit Swiss has caused havoc and we still had 2008, in which Nobel Prize winners and the entire US mortgage industry behaved badly and nearly brought down the global systems.
So, brilliant as they were (I'm biased but I think they have been) they could not solve mark to market.
Now, back to TSLA. Part of the market to market issue complexity is the stuff of which this thread is built. People here devote inordinate energy and dedicated skill to value TSLA. We rant and rave about algorithm trading, short sellers and the rest. Now imagine a bank properly valuing such an investment! Imagine any volatile, rumor driven market, say, interest rate futures. Imagine properly valuing US Treasury fixed rate securities when nobody actually knows what future rates to be, so cannot actually know whether values are any given thing at any given market price.
We see that dilemma with cryptocurrencies too, of course and those as many others have GAAP solutions that standardize the errors.
So, frankly, after having had one of those Nobel Prize winners teach me market dynamics, and having had a very close look at Basel negotiations I can say definitively "I haven't a clue how to cope with this issue". That is true.
Were it up to me I'd prohibit insured financial institutions from taking and unhedged interest rate risk. I'd then establish Basel 4 style structure to refine credit risk evaluation and restrict types of risk they could accept. In short, I'd return to something quite like Glass-Steagall. Impact, absolutely, but much less opportunity for unrestrained stupidity or fraud.