Even though this is kind of a logical fallacy, let's go with the 6-month rule for Blizzard betas. Note that these are just my own predictions and could be definitely be wrong.
RoS beta started last week in mid-november, that indicates a possible 6 months before the release of RoS.
Sometime around May (Most likely May 20th to coincide with the 2-year anniversary of Diablo 3 Vanilla's release, I know that technically May 20th is not the exact date of D3's release, but it's the closest Tuesday).
Patch 2.0(Pre-Expansion Patch)
Now for the pre-expansion patch, Lyrilla started it could happen at anytime, but more likely around the 2-month mark prior to the release of RoS. This make it sounds to happen around mid March which also coincides with around the shutdown of the Auction Houses. So very likely on the March 18th Auction House shut off date.
PTR for Patch 2.0
Obviously there is going to be PTR before Patch 2.0 comes out and it has also been confirmed that there will be one. Typically based on D3's beta history PTR last roughly a month prior to going live, now with a big patch like 2.0 it could very well scale higher then this, maybe even 2 months or more.
Based on my earlier prediction of a mid-march release of Patch 2.0, I would further predict that Patch 2.0 PTR would be out around the 1-2 months mark prior. So this could be anytime in mid-January through mid-February.
RoS Beta, Expansion -> closed beta and possibly open beta.
First off, I actually kind of doubt that RoS would ever go open beta, but Blizzard could very well follow D3 vanilla and have an open beta weekend like they did in the past but very unlikely a full blown open beta.
Since RoS beta is already out but only to Friends, Family and Media it is still in the early stages and will eventually go towards a more expanded closed beta, essentially letting more people in who have opt-in via battle.net and later also give away keys for fansites such as Diablofans to give out.
I predict that they will probably start expanding RoS beta around December-January.