Engadget reporting possible Verizon shared data plans

Wonder if this is real, and if so, would current unlimiteds be able to add a line without losing the unlimited?

Doubtful - they sell unlimited minutes but family share plans are capped. Such offerings are designed to increase revenues, not have 4-5 friends/family consolidate $120+ on data plans into an unlimited plan costing half that. And if it's a SHARED plan, then you probably can't keep your unlimited since they are sharing your data.

Question is how much data they will give these plans. For $10, I'd love to put my parents on this, but I'm not giving up unlimited data.

Also, expect a variety of such initiatives, all designed to ultimately get people OFF of unlimited plans. VoLTE is going to be a big incentive to swtich, along with what I presume will be a number of related options. VZW is very much under threat on it's voice services as VoIP options become better quality and more reliable. Google voice has undoubtedly taken a chunk out of their text revenues (they no longer offer a $5 250 text plan....min is now like $10 for 1000 or something).
I have an older plan with 6 lines sharing 5200 mins of talk and unlimited text and data. I would love to be able to add two more lines but it's capped at 6 lines. Every time I go into Verizon they are shocked I have such a good plan. It always seems they reduce benefits and raise prices. As Kodiak says, they want to get people off unlimited to increase profits.