How would this Madagascar which "pulled an Abyssinia" have developed, then?
Probably it would spend most of its time subduing internal resistance, which may require European assistance. Ideally, get a faction of traditionalists to kill a missionary or something, and then have the government request financial/material aid in defeating them. They could argue the traditionalists want to close off the country to foreign trade and ships, which may get some attention. What they don't want is the perception the government is being propped up by Europeans, so ideally any direct European intervention should stay confined to the port cities the Europeans will want to have.
I think they'd be close to Japan (island nation recently unified at risk of European colonialism), and possibly do even better at it than Ethiopia. They'd likely play up their Asian heritage (the Merina are lighter skinned than other Malagasy groups) to appeal to both Japan (as their Asiatic brethren) and the Europeans (since Africans were considered inferior to Asians in the racial pseudoscience of the era). IIRC this isn't too far off from what the Merina OTL practiced, and in any case not hard to see it evolve as a consequence of modernisation and need to appeal to foreign powers. The social consequences of this are obviously not pretty.
They'd likely have some grief with France over the Comoros. There are Malagasy-speaking people on the islands, and the islands were raided by the Malagasy into the 19th century. French influence started early in the 19th century, so this will be a sore point in relations with the French. The ideal scenario is for France and Britain to remain enemies into the late 19th/20th centuries, and Malagasy soldiers play a key role in attacking the Comoros and Réunion alongside the British--potentially they could get at least the former after a peace treaty. If it's like OTL and the British and French remain allies, then I don't think the Malagasy will make any aggressive moves--the consequences would be too great, and potential allies like Germany or Japan are too far away to aid. If Portugal does something stupid (like over the Pink Map issue) and gets diplomatically isolated, then possibly the Malagasy would fight them in a war. Call it the Russo-Japanese War in miniature.
Ignoring butterflies, then by the 20th century I think Japan will be an increasingly important supplier to the Malagasy military. They could easily go navy-focused and build a disproportionately sized navy for their country. So maybe a few coastal defense ships (like Thailand) ordered from Japan, some destroyers, some torpedo boats. Overall they'd likely have a mix of (dated by the time they get them) British and Japanese equipment.
By the mid-20th century they can easily be an important regional power and major player in South/East African affairs, but may have some serious internal issues over the oppression of peasants/caste system. Assuming a reasonable compromise is found and things don't go to utter hell (i.e. Mao/Pol Pot-style government), Madagascar is likely to end up a middle-income economy with a GDP per capita of maybe 5-6,000 and a population similar to OTL but with a more balanced population pyramid more similar to Southeast Asia (as better medical care and reduction of infant mortality would have occurred earlier)--so this means an economy about 10 times bigger than OTL, and about the size of OTL Ukraine.