Taylor and Turner are solid talents, but expecting them to slot in as ready replacements for Span/Desmond is a bit of a stretch.
Rendon/Harper is a solid core, but there are a lot of iffy bits (Zim, Werth, Ramos, Escobar, Espinosa) betwixt.
Scherzer is what he is, but then you've got Strasburg, his health, and impending FA in 2017.
Gonzalez is basically a 3 on a good day anymore.
Giolito looks like a phenom, but is still a wild card.
Other arms are nifty, but no apparent game changers.
I'm with dak, 2015 is a key year for WAS. It bodes well for Atlanta if Rizzo coughs up a couple of top prospects for a Chapman (or even a Kimbrel, given the strain it would ultimately put on a payroll which will need to add in 2016 and 2017).
They have gotten pretty much nothing from Span and Desmond this year so based on a straight comparison of 2015 to 2016, they will almost certainly provide a higher WAR. Comparing to 2014, they would need to provide 8 wins, which isn't happening. Taylor is on base for about 3 wins this year, which is probably about right with his defense in center field. Turner will provide speed and play solid defense, can't imagine him being under a 2 win player.
They got 25 WAR combined from everyday players in 2014 and 23.2 in 2013. So, with starters, they are probably shooting for 23-25.
Harper- 7 (?)
Rendon 4.5
Escobar/Espinosa/Turner- 5
Taylor 3
Ramos 1.5
That leaves about 2-6 or so to get from Werth/Zimmerman. I think they will be fine position player wise. Catcher being the biggest weakness, but just about every team is struggling at catcher. Werth/Zim will be injury concerns going forward, Im sure.
I'm not a big fan of Gio, but somehow he seems to put a mid 3 ERA up, which is fine for a number 3, which is what he will likely be.
Lopez is a potential game changer, but is far away. Joe Ross is putting together a handful of interesting starts and appears to be making a case for the rotation. I can't believe they got Ross and Turner for Souza.
As I mentioned earlier, they have 40 million coming off the books to upgrade at certain spots. Maybe another starting pitcher; maybe a catcher.
Right now they are on a 87 win pace while getting nothing from Rendon, Zimmermann, Fister, Werth, Strasburg.
Projecting to next year, they potentially lose:
Span- 1.4
Desmond -(0.2)
Zimmermann- 2.5
Fister 0.2
Total- 3.9 war (compared to this year so far)