One charger at one end and one electric locomotive at the other end?Do they? AFAIK, the contract was that there needed to be an upgrade path for electrification. IIRC (and please prove me wrong if you have evidence to the contrary), Siemens plan was that should electrification be necessary, the Chargers could be replaced with electric locomotives.
Probably the best solution considering that electrification will take a long time and will be partial. In addition, bi-mode electric/diesel locomotives tend to be more expensive than their non bi-mode counterparts, at least based on the cost AMT had to pay to buy them from Bombardier.