What are the (key) limits of coverage of Medicare for All?

Question

I don't live in the US, but rather in a country where there's a state mandated, single-(state)-payer universal health insurance - with additional layers of coverage for additional insurance fee through the health care providers.

As an example, some types of coverage which are outside the universal, state-mandated basis where I live: Dental care; various more-expensive medications outside the "medicine basket" (never mind the details); reimbursement for privately-arranged surgery as opposed to surgery in health-care-provider-affiliated / state-owned hospitals; second-opinion consults; discount on various medical devices and so on.

My question: What are the main limitations (qualitative and perhaps quantitative) on the coverage the US "Medicare" scheme as it currently stands (compared to complete coverage of any and all medical expenses)?

Notes:

• I'm not asking about whether these bills will pass, nor about how this is going to be funded, nor about the interaction with insurance companies and how that would change.
• Limitation can, however, be procedural, e.g. "you can only undergo certain medical exams if your own doctor's referral is approved by some review board, which often fails to approve" or "You can only see certain doctors rather than any licensed one" etc.
• I realize this can be described in minute detail; don't bother doing that - be a little more general.
• If you can also note which of the limitations are planned to be removed with the HR 676 Medicare-for-All bill, that would be nice.

Answer 1

Limitations of Medicare Parts A and B:

1. Only applies to people age 65 and older.
2. No dental or vision coverage. (Although see Medicare Advantage and supplemental plans.)
3. No long term care (e.g. in a nursing home).
4. No prescription drugs. (Although see Part D and Medicare Advantage.)
5. Deductibles and copays. (Although see Medicare Advantage and Medigap plans.)
6. Hearing aids. (Although see Medicare Advantage.)
7. Medical care overseas. (Although see Medicare Advantage, Medigap, and travel insurance.)

Mostly taken from 7 things Medicare Doesn't Cover, although I added the age limit and combined dental and vision. See also What Medicare Covers. Medicare Advantage is also called Medicare Part C and is an alternative to Parts A and B where Medicare and the enrollee pay the premiums to a private insurer. Medigap is supplemental coverage through a private insurer designed specifically around Medicare (i.e. people not covered by Medicare wouldn't buy it). Travel insurance and dental/vision supplemental plans are simply private coverage.

According to Wikipedia, Bernie Sanders' plan:

the "parallel" proposal by Sanders had significant differences, including a "global budget" system for hospitals. Both the proposals include expansive coverage including long-term care and dental care with no cost-sharing such as coinsurance, deductibles, or premiums, which as of 2019 is unprecedented in the world.

and later

Prohibits a private health insurer from selling health insurance coverage that duplicates the benefits provided under this Act. Allows the private insurers to sell benefits not medically necessary, such as cosmetic surgery benefits.

and

According to Robert Moffit, per section 303 of the legislation, if any doctor provides any private service outside of the government plan, the doctor may not bill the government for any service for any reason for one year.

These don't say it explicitly, but I understand them to remove the age limit and to eliminate Medicare Advantage plans. Medigap and other supplemental plans would remain for things not covered.

I'm not going to try to explain the differences between Sanders' plan and other plans with similar goals. There is some information about that on the Wikipedia page if you're curious.