After following along with TLE for some time, I've formulated a possible theory of its broader significance to the show. I would be very surprised if Thomas Mittelwerk ever appears on Lost. The reason is that the events of TLE are meant to parallel those that gave rise to the Dharma Initiative. In this way, TPTB can offer us indirect hints about the backstory of the show.
Basically, I believe Mittelwerk is following much the same path that Hanso did during the 1960's. After the latter's disappearance, the former took control of THF and discovered its experiments regarding the Numbers and Valenzetti equation. Like Hanso before him, Mittelwerk concluded that the world was in imminent peril and began planning for catastrophe.
The Spider Protocol is basically an updated version of the Dharma Initiative. TM has commissioned a massive expedition to a remote island where he will build a utopian community meant to weather whatever terrible fate awaits the rest of humanity. The blood replacement was either to prepare him for cryo-sleep (so he can doze through the apocalypse) or to cleanse him of disease (so utopia is as healthy as possible).
Or something like that...