In this statement, [X] is the subject of will be possible. But it's not [X] that will be possible.

What will be possible is for X to be used here as Y, the infinitive complement.

In other words, the sentence

• For X to be used here as Y will be possible.

is the original source. This can be Extraposed

• It will be possible for X to be used here as Y.

But the subject [X] can't be Raised, because the predicate possible doesn't govern Raising, with either an active or a passive infinitive:

• *X is possible __ to be used here.
• *X is possible __ to go here.

and it also doesn't govern Tough-Movement, which would extract an object instead of a subject:

• *X is possible to use __ here.

There are predicates that will work in these constructions:

• X is likely to be used there.
• X is likely to go there.
• X is easy to use there.

But possible is not one of them. Change the predicate and you change the constructions.

In this statement, [X] is the subject of will be possible. But it's not [X] that will be possible.

What will be possible is for X to be used here as Y, the infinitive complement.

In other words, the sentence

• For X to be used here as Y will be possible.

is the original source. This can be Extraposed

• It will be possible for X to be used here as Y.

But the subject [X] can't be Raised, because the predicate possible doesn't govern Raising, with either an active or a passive infinitive:

• *X is possible ... to be used here.
• *X is possible ... to go here.

and it also doesn't govern Tough-Movement, which would extract an object instead of a subject:

• *X is possible to use ... here.

There are predicates that will work in these constructions:

• X is likely to be used there.
• X is likely to go there.
• X is easy to use there.

But possible is not one of them. Change the predicate and you change the constructions.

In this statement, [X] is the subject of will be possible. But it's not [X] that will be possible.

What will be possible is for X to be used here as Y, the infinitive complement.

In other words, the sentence

• For X to be used here as Y will be possible.

is the original source. This can be Extraposed

• It will be possible for X to be used here as Y.

But the subject [X] can't be Raised, because the predicate possible doesn't govern Raising, with either an active or a passive infinitive:

• *X is possible __ to be used here.
• *X is possible __ to go here.

and it also doesn't govern Tough-Movement, which would extract an object instead of a subject:

• *X is possible to use __ here.

There are predicates that will work in these constructions:

• X is likely to be used there.
• X is likely to go there.
• X is easy to use there.

But possible is not one of them. Change the predicate and you change the constructions.

In this statement, [X] is the subject of will be possible. But it's not [X] that will be possible.

What will be possible is for X to be used here as Y, the infinitive complement.

In other words, the sentence

• For X to be used here as Y will be possible.

is the original source. This can be Extraposed

• It will be possible for X to be used here as Y.

But the subject [X] can't be Raised, because the predicate possible doesn't govern Raising, with either an active or a passive infinitive:

• *X is possible __ to be used here.
• *X is possible __ to go here.

and it also doesn't govern Tough-Movement, which would extract an object instead of a subject:

• *X is possible to use __ here.

There are predicates that will work in these constructions:

• X is likely to be used there.
• X is likely to go there.
• X is easy to use there.

But possible is not one of them. Change the predicate and you change the constructions.