The teaching of Shakespeare should be compulsory.

Shakespeare wrote a long sonnet sequence and many, many plays. To suggest that there isn't variety within his oeuvre is to be patently ignorant about the greatest English poet ever to have lived. 
 
If a teacher doesn't have the ability to apply their skills learnt reading Beckett to reading Shakespeare, one questions why they are teaching at all.

Teaching is best done when teachers know what they're talking about. Making teachers present material on certain subjects is dangerous in interpretive subjects like English, where teachers may not really know what they're talking about. Shakespeare is not a compulsory part of many English degrees, so the teacher may not be as good on Shakespeare as he is on other, equally deserving, poets, thus lowering the standard of teaching.

Pupils get the most out of school when they enjoy what they're doing. A teacher, similarly, teaches best when they enjoy what they're doing. Having subjects imposed on them erodes their ability to teach in a subject like English; allowing them the freedom to tailor their lessons to their own passions and the abilities of their pupils allows for more creativity in the classroom, more enjoyment for everyone, and overall a better quality of education.