TL;DR: For Weapon Exilus Slots, Reload speed should not be omitted, since the "benefit" it gives to Sustained DPS is negligible.
On the most recent Devstream I saw that the decision had been made after "internal testing" to remove mods such as Reload Speed (i.e. Fast Hands) from the Weapon Exilus pool. While I understand their intentions behind this, the decision is not backed by Warframe Exilus. Let me elaborate:
DE stated that they wanted the Exilus slot to be a "Quality of Life" slot. Something that had no real bearing on the effectiveness of a Frame or Weapon, that just makes it easier to use with certain playstyles. I would argue however that Reload Speed is such a minor increase in lethality that it shouldn't be excluded. While I agree that reload speed does allow for a marginally increased sustained DPS, it's effect is so negligible that it really isn't worthwhile excluding it. Other Exilus mods exist such as the Drift mods which give a Warframe a slight increase to it's strength or range, for example. This itself increases a Warframes damage, whether it be individual damage or area damage, albeit only marginally so why should weapon Exilus mods be any different? You could also make the argument that Magazine Capacity increases the sustained DPS of a weapon since it allows for less down-time between reloads; Silencing a weapon allows for a reduced Threat level, reducing the likelyhood that enemies would target you over other viable targets such as allies or your Companion, and allow you to maintain Stealth Multipliers more effectively; Coaction Drift can flat out increase the bonus damage given by Auras such as Rifle Amp or Steel Charge; so why aren't they removed from the Exilus pool? All of these have some affect on gameplay and damage, however their effects are so marginal that they should not be considered worthwhile removing...
Using warframe-builder.com as a guide, a completely standard Braton with a maxed rank Serration would deal 429.528 Sustained DPS, whereas the same weapon with nothing else but a Primed Fast Hands added would deal 476.935 Sustained DPS. In practice, this difference would barely be noticeable since the difference is only 47.407 DPS, and definitely wouldn't "break the balance of the game" since enemies such as Grineer Heavy gunners, at their base, have 300 health, which obviously scales based on enemy level.
Now obviously I'm not about to turn on DE if they ship The Old Blood with Reload Speed omitted, it's just a petty gripe of mine after all, but I think consistency is important. If Warframes can have Exilus mods that can increase their damage potential slightly then why shouldn't Weapons too? As I've said already countless times, their effects are so small that they really wouldn't be an issue. Plus, it'd be extremely nice to have some extra reload speed on Weapons with long base reload times since Warframe is such a fast-paced game as it is.