A blogger cites a 1962 study as noting that Taiwan’s first periodical, a Presbyterian newsletter, was in romanized Taiwanese.

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Táiwān dì-yī fèn bàokān shì 1885 nián chuàngkān de Táiwān fǔchéng jiàohuì bào, yóu Zhǎnglǎo Jiàohuì chuàngbàn, cǎiyòng Táiyǔ Luómǎ pīnyīn wénzì, bàodǎo jiàohuì dòngtài （Pān Xiánmó, 1962）.

It’s also worth noting that the roman alphabet was the first real script of Taiwan, the Dutch colonialists having developed a means for writing one of the language of the Aborigines. This script continued to be used for hundreds of years, though by relatively few people.