WI: An Austrian Queen for Umberto I

In a move to attempt to smooth tense relations between Austrian and Savoy, a match between Crown Prince Umberto I of Savoy, Archduchess Mathilde of Austria-Teschen was offered as a bride. Unfortunately, the Archduchess had the misfortune to indulge in a rather fatal cigarette, and her outfit caught fire when trying to hide it from her father.

With the death of Mathilde, Umberto married his cousin, the Princess Margherita of Savoy-Genoa. So, say Mathilde's father had been running late (enough for her that she could finish the cigarette) or even early (that she was not able to light up in the first place), and the marriage had gone through.

How might this affect Austro-Italian relations in the future? AFAIK the Catholic houses of Europe were not eager to allow their daughters to marry into the house of Savoy after seeing what had happened to the various branches of the Bourbons and Habsburgs.
Talk about a stupid way to die!
Since she died very young, it's difficult to forecast with any accuracy what would have become of her, and what influence she might have on Umberto I if the planned marriage had been finalized. However his father was Albert of Habsburg-Teschen, very conservative and a notorious anti-Italian (in the 1870s he campaignedmore than once for a pre-emptive war against Italy): this would be likely to reinforce the traditional education that she would have received as an Habsburg arch-duchess. OTOH, this generation of the Habsburg dinasty produced a few oddballs, and Mathilda might be one of them. In any case she could not be more conservative than the OTL wife of Umberto, his first cousin Margherita of Savoy. The marriage would have been quite a surprise for many, since Piedmont and Austria had fought three wars in just 18 years (1848, 1859 and 1866) and the house of Habsburg was certainly not much liked by Italian nationalists: it might be another problem for the young queen (or maybe not: a lot would depend on her behavior at court and in public. The pope would not have been pleased, that's for sure: Pius IX was still smarting from the annexation of the Papal territories in 1860 and would have considered such a marriage a further betrayal, this time perpetrated by the house of Habsburg. I would expect that the Non Expedit would still be published on schedule in 1868, and would be even more strong in forbidding the participation of Italian catholics in the political life of the kingdom.

Looking at the POD with rosy-tinted glass, the marriage might succeed in improving the relations between Austria and Italy (say the young queen delivers a couple of heirs by 1870, and makes a visible effort to learn Italian and woo her new subjects), and this might create some interesting butterfly in the relations between Prussia and France, including the OTL war of 1870 (in particular if Louis Napoleon manages to firm up the treaty he was pursuing between France, Austria and Italy). I'm a bit of a skeptic: there are too many conflicting claims between Austria and Italy which could not be simply swept away by a royal marriage, and the Franco-Italian relations are still marred by the Roman Question. However the Ausgleich of 1867 showed the the K-u-K was trying to reverse some traditional policy which had brought up the disasters of 1859 and 1866 (and the big scare of 1848) and this marriage negotiation might spring out of the same mindset: something good might come out of it after all. As a minimum, the diplomatic isolation of Italy would be reduced.
Well, I was thinking about Umberto's OTL consort: Margherita of Genoa. Both her and the duke of Aosta were proposed for Prussian matches - him to an unspecified Prussian princess and her to Prince Karl of Hohenzollern-Sigmaringen AKA King Carol I of Romania.

With an Austrian queen, and two relatives married into the house of Hohenzollern, how might this affect Italy's stance in Europe?
Basing it on family alone, Italy would probably look more to Prussia and Austria than it would to France, and the Triple Alliance might be more secure.

Be interesting to see if it would have any impact upon Amadeo's nomination for the Spanish crown.
Royal marriages have never influenced too much relations between countries, even when monarchs were absolute. Much less they can influence diplomatic relations in the second half of the 19th century.
Either there is a significant change of foreign policy in Austria (which was never there IOTL, even when Italy was a member of the CPs, from 1881 onwards) which might really smooth down the tensions between Italy and Austria or there is not. A royal marriage might be a signal that a change might be under consideration but it's still not the change.

Marriage links between Hohenzollern and Savoy would have to be regarded in the same way.

In 1914, the king of England, the kaiser and the czar were first cousins (and the last two still enjoyed significant personal power, in particular the czar) but this had very little (if any) effect on the events that brought Europe into WW1