Tenno Types

To allow consistent usage of characters from before Update 18 (where Operators were revealed) to be used together with Operators and Transference-Controlled Warframes, we came up with a headcanon that, albeit in no way, shape or form suggested by DE's lore, does not conflict much with the current facts we get from in-game:

There are 2 different ways for warframes to be made, and Tenno with skills matching one of them more than the others. The reason for these different "Warframe Types" would have been a combination of technical limitations, advances in transference technology, and the Tenno's personal affinity or preference. Since Tenno who are used to one type of warframe will require extensive time to get used to another kind, the type of warframe that a Tenno is best used to is referred to as their "Tenno Type". It can be changed with work, but only few put in the effort.

Mark 1
The Mk-1-Frames are a suit of armor to their operator, as most Roleplayers assumed before The Second Dream released. A single Operator may equip different frames, with respect to bodytypes that may make certain frames incompatible with most Tenno due to their build or general inhuman anatomy (e.g. Caliban). Due to being places physically on the battlefield, the personal risk for the Tenno is far greater.

Playing a Mk1 Tenno is very intuitive, as we can all imagine being put into a tight suit/armor and suddenly be superpowered.

Mark 2
Mk2-Frames are the ones that The Second Dream Quest & following quests introduced us to: Operators that use their Void-Powers (and possibly a Transference Chamber) to control their warframe/s from afar.

Playing as a Mk2 Tenno is a bit more complicated because we have to assume a multitude of workarounds to make your typical RP work. Operators can speak through their warframes via a speaker in the helmet, and the link between warframe and Tenno is capable of harming the Operator in case of heavy damage to the warframe (near-death-experience), or situations as they occured during the War Within Quest. Not all Tenno have to have access to all the powers that we see in game. Some Tenno might have good control over their void powers and not need a transference chamber (Post-TWW state), while others rely on a Chamber and are not able to use focus-powers. With our headcanon, these are not 'conflicting facts', but instead just different person's strengths and weaknesses. Mk2 Tenno tend to have a better control over their void-powers, while being physically weaker than the Mk1 Tenno who get a lot of exercise in the field.