Ok, not sure if any of this is true or official, but here's my input:
1) Your plan is going to stay the way it is for now. They won't just tell you next month, hey, pay $70 now. Unless you make a change in your billing, you'll be on whatever plan you are on.
2) I'm pretty sure that this is for new plans only. Remember the 4 for $100 promo? I know people who've had that plan from wayy back when they first had the promo. As long as they don't make changes to the plan, it's ok. So if those 4 accounts stay active for 10 years, they'll still be on that 4 for $100 plan. They get grandfathered in. If one of the accounts cancels, then the other plans do have to change to a plan they can qualify for, but if those accounts stay intact, then they'll stay that way.
3) The only issue would be is if you're on a single line plan and wanted to add another line. You won't get the $5 discount on the first line. Your 2nd line you add will get a $5 family line discount, but not on the $60 plan because you would have to change it to the $70 unlimited family plan -> $65.
4) The grandfathered plan is only temporary. When you upgrade your device (not 100% sure), you do an MEID change, and they'll have to select a plan for the device, and I'm not sure if your old plan will be on the list of plans for the new device. I haven't worked at metro in a while so I forget if it's possible to keep the same plan. Maybe if they call DSG (or *228 for you guys) they can get it done.
I agree though. This is getting to the point where metropcs is no longer a budget carrier. I used to have pride that metropcs is almost as good as the other carrier at a low cost, but $70 is pretty high. Truth is Verizon plans are in the $120+ range and it's not unlimited data (4GB with their promo, 2GB without), but metropcs is far from VZW status. Also, 5GB for $60 still beats competitors. 2.5GB for $50 does as well. I think they should tier it differently by getting rid of the $40 plan, and go $50, 55, 60, but I'm sure the people on $40 would complain about that, but really I think they should just make $40 plans for non-4G and make them run off 3G towers.
5GB of data is a lot for the average user, however there are users who stream video that will hit 5GB in a week. I think 10GB for $60 is a better allowance where medium-heavy users would fit in. There aren't many users in the 2.5GB-5GB range but $55 for that seems fair, however if you are a user that uses more than 10GB a month, you should kind of pay more $70 which also allows legal tethering? It's pretty lame that metropcs is just basically following in the footsteps of their competitors and no longer Unlimiting us. I'm really under the impression that the bigwigs at metropcs's marketing department is really dropping the ball in figuring what the consumer demands and is just copying what the other companies are doing. It's obvious with their Samsung Craft, ZTE Score, HTC One V, and stupid add-ons like metrobackup on android, myextras, metrostudio video, rhapsody, metronavigator, loopt, metroappstore, etc that they are new to this concept of Android devices and are years behind on understanding what consumers want. Ok, my thoughts are wandering off into a rant so I'll stop myself here.