Scrape XML files into RSS feed as input for IFTTT
According to your ideas - you should also consider using WordPress core code to fetch the XML data.
Create a plugin which will load XML data using HTTP API and call proper actions on your blog (in this case IFTTT will be unnecessary for publishing blog posts based on the XML data).
The only issue which you can have is a fact that you will need an access to the server cron - as wp_cron by default is called only during the users visits - so on the website with a small traffic it won't work as you can expect (it won't be called as often as you need).