Recent data from ExIm site Zauba reveals a Lumia Tablet under testing in India. This tablet will come with a Keypad and there are as many as 253 Tablets imported to India for testing purposes in one lot. So, it may seem that Microsoft may be preparing a new Lumia Tablet for launch in coming months, as Lumia 2520 is already near maturity in its product life.
With a recent leak revealing that Lumia 2520 is coming to T-Mobile, there are faint chances of the Tablet in question to be Lumia 2520, but this still seems bit unlikely to me at this stage. Recently evleaks has claimed that Microsoft may replace Surface branding with Lumia. Such move may make sense with Lumia brand having much appeal than Surface amongst common buyers.