As a reference point a couple of quotes from the M5V planning report:
"The King-Spadina area has been very successful. There has been significant reinvestment and development in the area and there continues to be a wide range of land uses. Notwithstanding this success there have been challenges. In particular, new development in the area east of Spadina Avenue is challenging the built form expectations of the Plan."
"... identify King Street West as being the most complex on the basis of its role as a transit route supporting two-way streetcar service, the variation in lot characteristics between the south and north sides of the street, and the historic main street character of the south side of the street. The scale and character of the historic buildings and retail activity on the south side of the street should be maintained."
"Relative to built form, the consultant evaluated the current built form environment relative to the original intent of the King-Spadina Plan. The report concluded that, for the most part, development has maintained the intent of the Plan. However, there have been and continue to be development applications in the area east of Spadina Avenue, on and south of King Street West which challenge the intent that new development would reinforce the scale and character of the
area’s historic buildings. The review concluded that there may be potential for building heights in excess of the existing planning framework but likely only in limited locations and in all cases subject to certain site conditions. Many of the recommended site conditions recommended by the Review study are consistent with those in the City’s Tall Building Guidelines. Additional conditions proposed by the study and recommended to be incorporated in the King-Spadina Secondary Plan are that such proposals demonstrate that they would not impact adjacent sites or the public realm and incorporate an increased stepback from the podium to the taller building elements."
"The King-Spadina Urban Design Guidelines are intended to support the implementation of the King-Spadina Secondary Plan. King Street West, west of John Street, is identified as a Special Street in the guidelines on the basis of the relatively continuous frontage of three and four storey buildings from the late 19th century along the south side of the street. The guidelines expect that new infill development on the street will respect and reinforce the built form character established by these historic commercial buildings in terms of building type, height and character along the street frontage, vertical and horizontal articulation and use."
My personal thoughts are to intensify the various lots north of King, but I agree with the city that the 19th century frontage and character of the south side of the street should be preserved. There are very few (if any) areas of Toronto that are like the south side of King West and these areas should be protected. M5V if built as is could be the first domino to fall on the south side of King.