EDIT on 3/25: No more rumors! Called in and was told the portfolio of new plans, as following:
$45 Simply Prepaid with 4GB data at LTE speed
$55 Simply Prepaid with 6GB data at LTE speed
$75 T-Mobile One with unlimited LTE data, unlimted 3G tethering, 200MB roaming data.
If you like whatever plan that is currently available, grandfather it in today!
That is, switch to whatever plan you fancy in your online account, and keep your account active (sufficient funds). If you like to keep the legacy $30 Walmart plan (100 min, 5GB LTE data), you need to call CSR (at 611) to switch manually.
Today I called T-Mobile CSR and confirmed that new plans will kick in this Sunday, 03/26/2017.
T-mo CSR didn't want to "spoil alert" me with details about "new plans". But the long lasting popular $30 5GB Walmart plan is probably phased out according to rumors below
I don't really care about other T-mobile plans, so mainly a heads-up post for those on the $30 plan, and whoever been hesitating - grandfather it in before 3/26
My best hope is that T-Mobile still keeps it alive, but after recent changes in their prepaid plans and their retail partnership with Walmart, I'd prepare for the worst.