A few thoughts (as an MD). Many medical schools are reluctant to accept nurses. Maybe not fairly, but it is not a common path. This will limit your choices.
Let's do some math on the next 10 years taking 2 different paths. I'm going to use big round numbers, and make some assumptions, but I'm pretty sure I'll get it in the ball park. We'll assume that you finish the BSN with no loans. It doesn't really matter because it probably effects both scenarios equally.
2018: Finish BSN, go to work as RN.
Move to Alaska (or substitute other undesirable, high need area). Sure, not everyone wants to relocate across the country, but this is equally as disruptive as moving for medical school.
2018-2019 Income: 100k/year, working a 40 hour week
2020-2022 Income: 150k/year, working 80 hour week (just like you would be doing in medical school)
From Jan 2018-June 2022: Total income $550k.
From June 2022-June 2025, keep working like a resident - 80 hour weeks will bring in big overtime RN pay. Collect another $450k
Scale back (and work like an attending physician) in June 2025-Dec 2027. Move to a location that you love, even though the pay is crap. $200k for 2.5 years of work.
Income Jan 2018-Dec 2027: 1.2 million, no debt.
2018 Finish BSN, apply to medical school.
Apps go out in June, so spend the spring doing MCAT prep, taking test, filing applications, fall interviewing. Cost $5k.
Work part time in 2018 in average RN market, make 30k.
2019 Accepted to medical school! Work full time for half the year, make 30k. Move somewhere. Pay a lot of tuition.
2019-June 2023: Lots and lots of medical school. No part time work allowed. Money only flows out. Cost: 300k
From Jan 2018-June 2022: Total income -$240k
Now it's June 2022 - You match across country! Move ($5k). Now you get a paycheck! It's 45k/year.
June 2022-June 2025: Work 80 hours a week, total income 135k.
Yay! You're done! You get a new job as a Family Pracitioner (or Internal Med doctor, or Pediatrician). You make $175k/year. (Maybe 120k, maybe 300k).
June 2025- Dec 2027: Income $437k
Summary: Jan 2018-Dec 2027: 315k in debt (the interest will not be tax deductible),make $632k.
Going forward, the physician job offers more annual income, but you've lost years of earning potential and accrued a ton of debt. Some smart mustache can figure out the compounding on the debt and the compounding on all the savings you start having when you are working as a nurse in 2018, but I'm gonna guess the difference is more than $1M. My opinion is that medical school is rarely worth it for a late entrant, especially one that has the ability to work at a high paying job now.