During the interregnum, after the death of emperor Maximilian, duke Ulrich of Württemberg had conquered the Swabian Free Imperial City of Reutlingen in 1519, something which wasn't allowed during an interregnum. The Swabian League, which was a defence alliance, then sought to overthrow the duke, which had aggressively had a attacked a (fellow) member Reutlingen. In order to pay for their campaigns they had to sell the duke's (former) lands to the Habsburg, which they did after a successful campaign in 1519. ]
Initially the territories were held by Charles V, but after the (inheritance) treaty of Brussels of 1522 (it adjusted the earlier (inheritance) treaty of Worms of 1521), Charles V wavered his share of Austrian inheritance, in exchange Ferdinand had to take over half of the debt left by their grandfather Maximilian.
As a part of the treaty of Brussels Ferdinand also gained Württemberg, though he only was formally enfeoffed with the duchy of Württemberg in 1530.
In 1534, with Ferdinand and Charles V being tied up elsewhere, duke Ulrich, with help of the landgrave of Hesse managed to regain his lands. In the following peace treaty, Ulrich had to accept getting his duchy as an Austrian fief; Württemberg would only regain Imperial Immediacy in 1599 (the bought it from Austrian Habsburg HRE Rudolph II, who kept the inheritance rights, if the male Württemberg line were to fail).
Anyway what if Ferdinand I of Austria was able to keep Württemberg for the Austrian Habsburgs. Will it have consequences for their position in the empire, will it affect the Reformation & Contra Reformation etc.? What are your thoughts?