A little late to influence voting too much here but:
A- Nominations:
Excadrill Yes
Compared to Landorus-T and Garchomp, its main competition, it's slower, harder to switch in, and has no Stone Edge to actually significantly damage flying types. However, it does have one perk that keeps it in A, namely Mold Breaker, but i don't believe that it's good enough to keep it out of A-. sand rush is also cool but since it requires having a ttar on the team (which exca can't eq next to, so the sand timer is ridiculously hard to refresh for it) thats kind of a buzz kill and not even A-worthy
Hitmontop Yes
See my earlier post on the subject
Scrafty Yes
see my earlier post on the subject
Genesect yes
it's too frail to switch in and relies on coverage to damage things. It's good at offensive pressure though and can spam u-turn like no other (except maybe lando)
Ludicolo yes
though it's a good generic attacker in rain, it's really held back by its abysmal physical defense. It's unable to switch in on any sizable neutral physical attack, severely limiting its utility, and suffers from 4mss
Conkeldurr
Latios ABSOLUTELY NOT.
Latios is one of two viable dragons in XY (the other being hydreigon) to resist both fire and water which is HUGE. Its typing allows it to serve as a generic catch-all for common special attackers (such as rotom-w and zard), its speed tier is excellent, and it covers almost all fighting types as well. Latios is a fifth or sixth mon I often find myself using because of its ability to check so many top threats in the Doubles metagame. Granted it has its downfalls—losing to steels being the main one—but in a meta with so many answers for steel-types that's entirely forgivable in favor of its pros.
Breloom Yes
As Darkmalice said, if it outspeeds both opponents, it WILL be the biggest fucking pain in the ass. breloom rofls all over the pwnemon special so i can appreciate its strengths. That being said, it is really frail and ive never been able to use it properly myself.
Shaymin-S no.
It's not even the sheer offensive presence so much as its effect chances. Seed flare is fucking AMAZING as an assist move when paired with another special attacker, giving a 68% chance to double your next attack's power, not to mention grass is a p. good attacking type atm. Air Slash is obviously hitler personified. It's the fastest non-mega pokemon in the metagame, so it definitely deserves a spot in A.
Rank Shift Nominations
Tyranitar down to A yes
Heatran down to A abstain
it has a ridiculously good set of resistances that let it keep coming in; however, the exploitable 4x ground weak is an absolute bitch to deal with, which makes it hard to keep in for long when every team has 2-3 ground move users. also, heat wave really doesn't seem to hit too hard imo, 3hkoing neutrals, which just isn't as much as i'd like to be doing. but it's a good utility answer to a lot of attacking types and mons. UGH CANT DECIDE.
Gengar up to A yes
Pinsir up to A ABSOLUTELY NOT.
Pinsir was on one good team, hooray. That doesn't make it A-rank; the poke is an absolute pain in the ass to build around and can't just be fit on any team. For one, its ridiculously poor typing makes it all but impossible to bring in (fighting and ground types, its two usable resists, usually carry rock moves) and for two, it is for all intents and purposes a mono-type attacker (close combat comes just short of koing basically everything it targets, and eq is shit lol, and it doesnt get megahorn). All this might be forgivable and worthy of A- were it not for one crucial detail: it uses up your mega slot. Have I ever found Pinsir worth using over another mega? No. I may sometime in the future, but if it were A-worthy, that probably would have happened by now.
Bisharp up to A yes
as for the other three: i originally nominated them so go read it niggas
edit: would it kill you people to provide some actual discussion in this thread, it feels like very few people contribute nowadays :(