Tiered masternodes is a new concept. It's like having different categories of masternodes with varying ROI.
For example, let us consider 3 tiers -
Tier 1 : Collateral - 10k , ROI - 200%
Tier 2 : Collateral - 25k , ROI - 250%
Tier 3 : Collateral - 50k , ROI - 300%
So, as the collateral increases, the rewards will also increase to compensate the investors. Roi is dependent on the number of masternodes running( More the no. of mns, lesser will be the Roi ).
Well tiered masternodes sounds very interesting concept, though I would be waiting for the official announcement, with detail info regarding masternode tiers, collateral and roi and few other things. Hope these details are posted on this ANN thread, so as everybody get to know about Traw MasterNodes.
Tiered masternodes are quite nice as it gives everyone the chance to set one up regardless of how deep your pockets are. It is a way to include as many people in the staking process as possible and not just have one threshold and that's it.