Trump, if he continues on his current trajectory, just might, however, deny Bush his expected Dem-state majorities and then the RNC would have to change the rules again or have no one oficially eligible for consideration at the convention which would throw it open to consideration of anyone at all. Even with that, the RNC controlled non primary chosen delegates could probably prevent any conservative from being nominated and a "compromise" for Rubio might well occur.
Portions of two of the rules to which you have mentioned:
https://s3.amazonaws.com/prod-static-ngop-pbl/docs/Rules_of_the_Republican+Party_FINAL_S14090314.pdf
THE RULES OF THE REPUBLICAN PARTY
RULE NO. 16
Election, Selection, Allocation, or Binding of Delegates and Alternate Delegates
(a) Binding and Allocation.
(1) Any statewide presidential preference vote that permits a choice among candidates for the Republican nomination for President of the United States in a primary, caucuses, or a state convention must be used to allocate and bind the state’s delegation to the national convention in either a proportional or winner-take-all manner, except for delegates and alternate delegates who appear on a ballot in a statewide election and are elected directly by primary voters.
RULE NO. 40
Nominations
(b) Each candidate for nomination for President of the United States and Vice President of the United States shall demonstrate the support of a majority of the delegates from each of eight (8) or more states, severally, prior to the presentation of the name of that candidate for nomination. Notwithstanding any other provisions of these rules or any rule of the House of Representatives, to demonstrate the support required of this paragraph a certificate evidencing the affirmative written support of the required number of permanently seated delegates from each of the eight (8) or more states shall have been submitted to the secretary of the convention not later than one (1) hour prior to the placing of the names of candidates for nomination pursuant to this rule and the established order of business.