First: the whining about the 100 series is so over. Please move on. It has no bearing whatsoever on any current products.
Second: no, Google has not abandoned nor neglected Google Voice. In fact, it has spent a fortune over the last few years, completely tearing out and replacing, or upgrading, its entire telephony infrastructure. The website and the Android and the iOS apps have been replaced, and the apps now receive very frequent updates. What's driving this, is Google's decision to offer a fully-supported, business-class, paid telephone service, integrated into its G Suite product. The revenue generated from the paid service will benefit the free consumer service, since they use the same back-end infrastructure. During the period since the old 100 series days, Google has completely replaced the old XMPP VoIP system with a new, standards-based SIP VoIP system. The website and the apps are now fully VoIP enabled, and the same system is used by OBiTALK devices.
Third: no, Poly has not discontinued the OBiTALK ATAs. Obihai was first bought by Polycom, then Polycom merged with Plantronics, to form Poly. The three companies' supply chain and sales channels needed (and still need) work to standardize on a product numbering (SKU) scheme, and of course, a new "branding" or logo.
Polycom and Plantronics traditionally sold through service providers or VARs, whereas Obihai sold through authorized retailers, such as Amazon, Newegg, B&H Photo, etc. Poly now has an integrated, business-focused product line of conference calling equipment, headsets, and IP phones. They are also selling the non-Google Voice enabled OBi 300 series.
They are maintaining the Google Voice products, and have simply rebranded them and given them a new black color and new SKUs. The products include the 200, 202 and 212 ATAs, and a few IP phones, from the 2000 series.
So: can anyone guarantee that the product you buy today will support open SIP standards for the long haul, sure. Can anyone guarantee that the product you buy today will support consumer Google Voice for the long haul? No, since it depends on the business decisions and roadmaps of two independent companies. The two companies have grown their partnership, and the first IP phones certified to work with Google Voice for G Suite are from Poly's VVX x50 series. Note: the OBiTALK consumer devices will not work with Google Voice for G Suite, and, conversely, the Poly IP phones will not work with consumer Google Voice.
What to buy today? For Google Voice, either the 200 series ATAs or a 2182 IP phone would be the solutions. For other ITSPs, especially for small business use, either the 300 series ATAs or one of the Poly VVX x50 series IP phones would be ideal. Remember, you would be buying essentially a small appliance, not an automobile, and the length of service life can't be compared at those two widely-different costs.
Consumer Google Voice has never been intended for business use, and it has no service level guarantee. If you want bare-bones, reliable but simple SIP VoIP service, look to the various SIP VoIP ITSPs such as Callcentric,
voip.ms, etc.
Here are three links to some of the current model, consumer Google Voice compatible products (note how the SKUs are still in transition):
https://www.amazon.com/Obihai-OBi200-Adapter-Support-Service/dp/B07FCS1NGM/https://www.newegg.com/polycom-2200-49522-001-accessories/p/N82E16833617016https://www.provantage.com/poly-polycom-2200-49620-001~7POL915L.htm